... Should I be concerned?

Look into the difference between gain control and volume control. In very, very simple terms, volume effects the outgoing signal but does not have any effect on the signal. It simply makes the signal “louder”. Gain control directly changes the amplitude of the incoming signal and has a distinct effect on the signal. The knobs on the back of your amp are gain, not volume. You can do something called “gain staging” where you do exactly what you are thinking and better matching the volume output to the amp gain and overall volume of the system. The trouble is when you “turn down” the gain knobs you are no longer getting the most out of your amp, plus adding potential noise into the incoming signal via the pot. With the knobs all the way to “max” they are effectively out of the signal path and your speakers are getting all the power the amp has. Play with it, see how it sounds. If you like the result, good to go. Otherwise, you may need to seek out a new preamp that is a better output level match for your amp.

To maintain the pots they need to be turned up and down several times to clean the contact

I thought I read all the way up, on Parasound.  Someone will chime in.
BUT clean the pots, for good measure. Every 6 months or so.

Regards

volume effects the outgoing signal but does not have any effect on the signal. It simply makes the signal “louder”.

😂 Clear as mud. And exactly backwards. 

Amplifiers are fixed gain. They multiply (amplify) input by a fixed amount. Volume controls are basically variable resistors. They trim or attenuate the signal. Where the volume knob is pointed, how far its turned, is one of the most irrelevant things in all of audio. If you think it matters, watch Spinal Tap until this sinks in. https://www.youtube.com/watch?v=4xgx4k83zzc

So no, you should not be concerned.

No, you should not be concerned.      You can either download or read the owner’s manual from Parasound, here: https://parasound.com/pdfs/vintage/hca750_1000om.pdf      You’ll find instructions, under Level Controls, on page 7.      Here’s a more detailed explanation, of what you’re facing: http://rftech.custhelp.com/app/answers/detail/a_id/471/~/what-is-an-amplifier-gain-control%3F#:~:tex...      Read the tutorials at the bottom of the page, for more insight.      You’ll note, if you read the Parasound manual; it mentions that the amp will sound best with the level control set to max.      That’s because at max, the control’s resistances (crappy traces, typically) are bypassed.      Only you can judge whether a lower setting matters, to your ears.

Try it and see what you think.  Just be conservative.  You can always put it back if you don’t like it.

I have gain controls on my old Mac 2105 which I adjust frequently so that I cn keep the linstage volume up to a certain level, and I have no issue at all with the sound quality. My tech told also me that it has no effect on the peak power available from the amp. 

A suggestion: Turn the Parasound’s level controls all the way down and your preamp’s volume knob to where you want it, at what you desire as your highest/max position.      If you can choose, do this procedure in Mono mode.        Play what you know to be a CD recorded at a high level, with a good center image.      Turn each channel’s level control up (slowly) to obtain your highest, typically enjoyed, listening level/SPL, with a solid center image.      Listen in Stereo mode.        If you don’t like the sound: like knotscott said.....

It kind of depends on the quality and performance of the volume pot in your unnamed tube preamp.  It might perform much better at or beyond its midpoint.  So the improvement here might outweigh the degradation of the signal at the amp.  Only way to check is to try it both ways and see which you prefer (if you can hear a difference).

Again, the manual recommends all the way up.. If not you have to clean the pots every now and then. They are not the best pots, BUT that is a great amp. All the way up...

Regards

Am wondering: since there are 2-12AX7s and 2-EF86s - could I change and/or control the preamp gain by changing to equivalent tubes (ex: would switching to a 12AU7 instead of the 12AX7 make a diff)?

twoleftears

Notice that when I set the volume knob on the preamp where I'd feel comfortable for usual listening (about 9 o'clock) - and adjusting the gain knobs on the Parasound's rear: I can decrease volume but there is very little volume increase turning the knob up and thru 12 o'clock: ?

".....would switching to a 12AU7 instead of the 12AX7 make a diff?"      Yes; in most cases, the 12AX7, 12AT7 and 12AU7 are interchangeable (gain factors of 100, 60 and 17 to 20, respectively).      That could actually be your best bet, but- check with your pre’s designer, first.

Put this Schiit SYS between your CDP and your preamp to lower the gain!
https://www.schiit.com/products/sys

If you want to lower the gain of the 12ax7 you might want to try the 5751 which is a lower gain equivalent

Also, here is the link to the Brent Jessee website's  12ax7 page , you might find his take on the different 12ax7 variants and brands helpful

http://www.audiotubes.com/12ax7.htm

@insearchofprat.....I am going to answer this from a different angle, and it is my experience, I say this. With the input level controls on the Parasound, set low, initially..............bypass ( do not use ) the tube line stage, and go direct from the Marantz SA 8001, into the Parasound. The SA 8001 puts out greater than 2 volts, and has one of the cleanest, least distorted output stages, and has a hefty, beefy, analog output stage / power supply, in an all in one cd player. Enough clean, hefty voltage, to drive your amplifier to full power. This will be " passive ", without the additional gain, to drive the power amp. Some posters here ( possibly all ), will disagree with me, on the passive mode, which is fine. I am suggesting doing this, for a week or so ( although it will be a pain to operate the rear controls on the amp ), because I have found, all line stages, especially tube products, to add colorations ( some say, additional warmth, smoothing over, just as a few examples ), and, robs you, of the finite details and information, embedded in your cds. This a a big controversy, between using a gain stage, and going " direct ", or " passive ", and I guess, you figured out, what camp I belong to. Lots of reading, here and elsewhere, on the subject. If you only listen to this one source, and you like what you hear, going direct, you can contact georgehifi, here, and get from him, possibly, the best " passive preamp ", in existence. Anyway, enjoy, stay safe, and be well. Always, MrD.

So many suggestions. Use your ears. We can't tell you what sounds best.
We're not there.

Lowering gain of power amp is a good thing.  Overall gain from the source to speakers will be the same, but spread of the gain will change.  More gain will be allocated to pre (quieter environment) than to power amp (noisier environment), not to mention reducing noise pickup by ICs (higher signal level).
 I don't know construction of Parasound, but even if gain is fixed and you just lower the signal (volume pot), the level of the signal entering the box will be higher (better for S/N).  Yes, engaging Parasound pots puts them in the signal path, but reducing authority of preamp's volume pot (max power=wider angle) is good.  I would do what rodman99999 recommended, unless you can hear audible difference.

The controls on the back of the amp allow you to adjust the input gain on the amp so that the volume control on the preamp can operate within its optimum range.  There is no rule that says that those amp controls should be full on.  You can also use them to correct for a preamp with a balance issue with a dodgy volume potentionmeter. 

Mrdecibel

When you mentioned "passive preamp", I think I have one sitting in the closet, presently unused (purchased used): Morrison ELAD. Why do you think that might be an answer in lieu of the Wolze (my tube line stage).

rodman99999

Designer Dave Wolze is somewhere in Calif and years ago I found out there we're only like 10 kits made before he lost funding to produce them. Got this vintage, used about 12 years ago from some dude who buys and sells what he finds in upstate NY,  had a falling out years ago and don't know how to contact him. 
In another topic discussion (which I'll have to look up), someone seemed to have a reference / familiarity  to the preamp, and told me it was originally designed for 12AU7s... I'd have to take it to a local, and could he determine what the actual layout is in the one I have, for which tube? Would it play if it was setup for 12AU7s with AX7s in it?

Q) "Would it play if it was setup for 12AU7s with AX7s in it?"      A) Yes, it easily could. As mentioned; those two tubes are usually interchangeable.               ".... someone seemed to have a reference / familiarity to the preamp, and told me it was originally designed for 12AU7s... "          That could very well be the issue(someone, along the line, trying to hot rod the pre).

btw:   What do you have to lose, by trying your Morrison?      I used to own a Placette Passive Volume Control.      Unfortunately; the rest of my system, at the time, didn't have enough gain, for the SPLs I enjoy, with many of my CDs and vinyls.   With recordings done at higher levels and no compression; I loved the transparency.    

Here’s a thread that mentions the Wolze as using two 12AU7s:      https://www.audioshark.org/pre-amps-9/wolze-triode-line-level-preamp-4421.html      Dave Wolze actually replied to the post and didn’t dispute the mentioned tube compliment.                             Confirmation, perhaps?

You never want your volume control to max out at a low volume point. You want your volume control to be anywhere between 4 and 6 if the volume control starts at 0 and the max would be 10. Check with your preamp/integrated manufacturer to determine what is the optimal setting. For example, there are many threads on how to balance the volume output of your dac into your preamp with the volume control setting of the preamp. My McIntosh preamp optimal setting for the volume control was with it running between 50-60%

I had a similar issue when changing to far more powerful amps recently. I could barely get volume knob to 9 o'clock without nearly breaking a window. Opened up my preamp and to check the gain setting dip-switches (options for 0, 6, 9, 12 an 18db) and they were at max 18db. Brought it down to 0 and it's back in business.

Similar situation to au_lait, but a digital eq and a matrix in lieu of a preamp. 

 In 'idle', no hums or noise....but one is aware that the 'false move' could be expensive and fretful....;) 

Measues are in place to keep that from occuring.  I like loud, but under control. *L*

+1 jnorris.  I would use the attenuators on the back of your amp to obtain the volume level desired using your pre as you wish. Then you could answer the question regarding any degradation in sound quality.

@ insearchofprat - Installing a pair of 12AU7 tubes, should result in (around) 1/5th the gain of the 12AX7 and correct levels to your power amp.      Be certain the tubes are tested and rated as, "Low Noise".

Look into the difference between gain control and volume control. In very, very simple terms, volume effects the outgoing signal but does not have any effect on the signal. It simply makes the signal “louder”. Gain control directly changes the amplitude of the incoming signal and has a distinct effect on the signal. The knobs on the back of your amp are gain, not volume. You can do something called “gain staging” where you do exactly what you are thinking and better matching the volume output to the amp gain and overall volume of the system. The trouble is when you “turn down” the gain knobs you are no longer getting the most out of your amp, plus adding potential noise into the incoming signal via the pot. With the knobs all the way to “max” they are effectively out of the signal path and your speakers are getting all the power the amp has. Play with it, see how it sounds. If you like the result, good to go. Otherwise, you may need to seek out a new preamp that is a better output level match for your amp.

huh?

Not knowing the amp specifically i will guess that they are simply a potentiometer (volume control) in-line between the preamp and the input of the amp. yes, they **could** control the gain (the amplification factor) of the amp - but depending on the design this has complications that most designers would avoid due to unknowns in the real world.
So... i'll guess that its nothing more than another variable resistor divider in series with your signal.  You therefore have two - one in the amp and one in the preamp.  You can turn either one, or both, down.  It really doesn't matter. If you turn on all the way up an d"take it out of the signal" as soemone said, you simply must put more of the other volume POT in the signal.  6 to one, half-dozen to the other.  Set it so its most usable and move on.  There are vastly more important things to worry about.
G

Thanks again to all. Be Well -Best Wishes...

@insearchofprat.......Every pro amp I am familiar with ( which is many ), have input level controls, so they can be set, as mentioned above by jnorris, and also, to create level matching, in multi amp / speaker setups. Although a good volume pot might be at it’s best, at max setting, it should be fine at any other level. The Morrison ELAD is a very simply designed unit, and is more of a " straight wire with gain ", as opposed to your tubed preamp. I have not heard an ELAD in years, but I remember being involved in a preamp shootout, comparing it, to much more expensive, well known preamps, both tube and ss, and it showed less character, less sound of it’s own, compared to the others. I would try it, as it costs you nothing, as pointed out by rodman. There is nothing wrong with enjoying tubes, or any active gain stages, in your equipment chain. I like what I like, and I understand, very well, the variety of equipment available, and, the individuality, of every listener. But, when additional gain is not needed, and the stars line up between components ( gain and impedance matched ), for me, nothing like a good passive unit ( I happen to use a top Luminous Audio unit ). It is up to each individual, the sq outcome they are looking for, and without using the ELAD, you can still experiment ( Marantz into the Parasound ), as you will, as well, be using 1 less set of interconnects. Whatever YOU like best, that, is all that matters. Enjoy, stay safe and be well !

Hello,
If these are gain controls instead of volume controls you will need to reset or adjust the gains using a meter. They need to be balanced with one another. They sound like gains due to how sensitive they are. No pun intended. Be careful you don’t mess up your speakers. Please disconnect all components from your amp before adjusting anything using the meter. 

@ insearchofprat - With the Wolze; you can roll 12AU7 tubes and tailor your sound, to your heart’s content.             From what I’ve read about the Morrison; you can enjoy some wonderful transparency.     Two very nice pieces/great potential.     Have fun and happy listening!

Took advice above to heart and removed the Wolze tube line stage; now playing CD direct into Parasound power amp: lifts a veil off the music, presents a leaner, more detailed and faster (I’d say more PrAT) sound.

Comparative Tunes playing: Rapture, Sunday Girl and Atomic by Blondie; Blue Eyes Cryin in the Rain, Can I Sleep in your Arms and Remember Me by Willie Nelson; Touch of Grey, Sugar Magnolia, and Franklins Tower by the Grateful Dead; Ready to Run, Sin Wagon and Hole in My Head by The Dixie Chicks; Alison, The Angels Wanna Wear My Red Shoes, Radio Radio, and Almost Blue by Elvis Costello & the Attractions; Sinatra’s 1958 version of Come Dance With Me; All I Want, Blue, and California by Joni Mitchell; Famous Blue Raincoat and Ballad of A Runaway Horse by Jennifer Warnes; Spinning Wheel and Blues - Part ll by Blood, Sweat and Tears; Carry On Wayward Son and Point of No Return by Kansas; Moondance, Wild Night, Full Force Gale and Brown Eyed Girl by Van Morrison; and others... Changes like this, so drastic and distinct, have you pulling out stuff you haven’t heard in awhile (and being WuhanVirus quarantined gives you dedicated time...).

Again thanks to all for input... I will continue to check for input from others, as time goes by...

The only possible drawback that I saw, was having two level knobs to adjust.      The simplest, shortest path, is generally the best sounding.        When all the stars are aligned, that is.       KUDOS!

Are you seriously considering replacing parts without simply turning the volume down and listening?  If you rears are that bad, buy some Bose speakers and a guitar amp.

Geez!