Setting up 2 power amplifiers to setup at once help?

I've never heard of an integrated preamplifier though there certainly can be such a thing. If you mean an integrated amplifer then it depends some have the pre outs to connect external power amps. 

Is it possible you use an integrated preamplifier with a power amplifier. In my case an integrated preamplifier with any of my denon or Yamaha power amplifiers ?

"So using the sub-out signal to drive the low frequency amplifier would cause frequencies between approximately 80 Hz and 125 Hz to be under-emphasized or even almost absent"

Good point, which is what I was trying to emphasize here-
"I can see a situation where the signal sent from the receiver is too 'low' for the difference between the frequency ranges of the low to mid speakers, which is why I advised to dial it up till it sounds full."

This is exactly why I didn't try it with my system since my stereo  crossovers are pre-selected at 60, 80 and 100 Hz and my speaker crossover is set to 125. I had thought an AVR would have a more flexible range. My mistake. 

not worth it.....even if done correctly

Looking at the manual for the AVR-2801, which can be found via a link near the bottom of this page, it appears that in stereo mode (i.e., when a surround sound LFE signal is not present) the bandwidth of the sub-out signal will extend up to a frequency that is fixed at 80 Hz. (See especially pages 16 and 17). While the crossover point between the low and mid/hi frequency sections of the speaker is at 125 Hz. So using the sub-out signal to drive the low frequency amplifier would cause frequencies between approximately 80 Hz and 125 Hz to be under-emphasized or even almost absent (depending on how steeply the filters roll off), although the relatively narrow difference between those frequencies would tend to mitigate the issue. Also, as the notes in the manual make clear, there are a number of menu settings that would be involved in doing that, creating opportunity for error.

So I would go with Imhififan’s suggestion of splitting the front right and left channel pre-outs to drive the two amplifiers. Although chances are the physical spacing of the two RCA plugs at the end of the particular cable he suggested is not enough to allow connection to two separate amplifiers.

So it can be done without and active cross over? And unidentical amps. Considering that @almarg has mentioned that the gains are almost identical ?

Yes, it can be done, and **if** the Denon amp (as well as the Yamaha amp) provides adjustable input levels you would have a lot of flexibility in balancing the volume of the deep bass with the volume of higher frequencies. Which might be helpful in dealing with room effects.

One additional possible complication that occurs to me, though, is the possibility that one of the two amps produces an output signal having the opposite polarity of its input signal, while the other amp doesn’t. That’s probably unlikely, but if that is the case the resulting sonics would likely be poor (although no damage would result). If that is the case, though, you could compensate by interchanging the + and - connections on **either** the low frequency or mid/hi frequency section of each speaker (but not on both sections).

In any event, just be absolutely sure that the jumpers are removed from the speakers if and when you biamp. If they are not removed you would be connecting the outputs of the two amps together via those jumpers, which could damage either or both of them, as has been indicated earlier.

Regards,
-- Al

"Imo, it's not a good idea, you don't want to use a active crossover in the receiver and the passive crossover in the speakers at the same time. "

I am curious why you think this. You are simply sending a signal that has passed a low-pass filter to another filter that should pass that signal (if set low enough). 

I can see a situation where the signal sent from the receiver is too 'low' for the difference between the frequency ranges of the low to mid speakers, which is why I advised to dial it up till it sounds full. seems like this method would allow you to better control the low end. 

On the other hand I see no issue with doing it like you suggested (as I have done both) except it is harder to control the 'amount' of low end. 

Might consider using the 2801 to power the highs for your speakers and the 'sub' out from the 2801 into the Yamaha to power the lows.

Imo, it's not a good idea, you don't want to use a active crossover in the receiver and the passive crossover in the speakers at the same time.
Use a pair of 'Y' rca cable connect the FRONT R/L pre-out to both power amp input.

https://ae01.alicdn.com/kf/HTB14A.3RpXXXXa6XVXXq6xXFXXXU/ATAUDIO-HIFI-Single-RCA-to-Dual-RCA-Subwoof...

Wow. A lot of things to consider. Appreciate all user comments and feedback. Probably going to do a bit more further reading and research before I attempt anything just to make sure I take every step with precaution and th advice you guys have given me. So it can be done without and active cross over? And unidentical amps. Considering that @almarg has mentioned that the gains are almost identical ?

Might consider using the 2801 to power the highs for your speakers and the 'sub' out from the 2801 into the Yamaha to power the lows. 

Make sure there is no bridge between the speaker inputs. 
If you can dial in the crossover freq. start at lowest and move up to level that works. If not available set front speakers to "small" (which I would do anyway). 

@almarg Thanks Al. Rock and roll!

I took a look at the manuals for the two amps in question, which can be found at hifiengine.com if one is registered there, and I calculated their gains based on their specified sensitivities and power ratings. In this particular case it happens that the gains of the two amps are almost equal, assuming the specs are accurate.

To be precise, the Denon’s calculated gain is 32.0 db, and the Yamaha’s is 31.24 db. Also, the Yamaha has input level controls, providing up to 20 db of attenuation in 1 db steps, and the Denon **might** also have input level controls. Input level controls on the Denon are "only provided for versions other than USA Canada and multi-voltage versions."

Finally, I took a look at the manual for the speakers and it confirms that they are suitable for biamping (when the jumpers are removed, of course), meaning that the low frequency and high frequency sections are not interconnected internally.

Regards,
-- Al

@noromance  I own enough amps and preamps to equip a store! I have my favorites, too! Same for speakers - their sonic signatures are certainly more easy to discern!

@noromance With two amps of different gains the bass and mid/high sound levels won't match! That would hardly make for good listening! The OP wants to give his father the Denon and keep the Yamaha for the Polk's. I personally would do the opposite! I think the Denon will sound a bit better than the Yamaha! You are right though - the OP should sell either amp and get something like a Levinson ML3. Then he'd need a real preamp to match - like an ML1. Next, better speakers and onward down the rabbit hole!

@roberjerman I think we've covered that. He could sell both amps and get a better single one that would be the best solution. But then again, you don't think amps sound different.
The guy wants to try it out, play, and learn and wants to check in if it's okay. It's low-end kit. Let the fun and learning begin!

@noromance The OP is a novice! My advice is correct! The two amps must be identical for bi-wiring to work properly! Let him install two jumpers per speaker and use just one amp at a time!

Yes, the top diagram is correct! Just get two jumpers (a few inches of wire will do) for each speaker. Forget about bi-wiring (the correct term). Use only one amp at a time with your two speakers - after you install the jumpers!

You understand what you are doing? Whether it sounds good or not, I am all for experimenting and learning. Sure, try it and see. You won't break anything unless you short out connections etc. That is your risk. Take care not to set the volume to max.

There should be jumpers between the two reds and the two blacks. Get them! You still cannot bi-wire the A7's because you don't have two identical amps.

Ok I know on the back of my speakers I have in total 4 connectors 2 pairs

so 2 red connectors and 2 black connectors. Do i really need jumpers ?

if I follow this diagram am I in th clear?

https://goo.gl/images/zhPV3u

Once again do do they need to be exact same power amplifiers ? Or in my case there different one Yamaha one denon? I know another user commented earlier on advising don’t do it. This is all just for experimental purposes but I don’t want to risk damaging anything either 

Again, to passive bi-amp (bi-wire) each speaker needs two pairs of connectors (with jumpers) on the back. This allows separation of the internal x-over into low and mid-high frequencies. I doubt the RTi A7's have this!

Want to hear a "different" sound from your speakers? Get a tube amp with high output impedance (over 1 ohm). Like a Prima Luna (output impedance of 8 ohms!). Or a single-end tube amp (low power and 3%+ distortion!).

I doubt that you will be able to hear any qualitative difference between the sound of the Denon vs. the Yamaha. All modern electronics have been pretty much sonically equivalent for the past 20+ years or so! Regardless of what the "golden ear" crowd claims! 

I have bi-amped two pairs of speakers successfully using an active crossover. Splitting the signal into bass and mid-high frequencies. One pair of speakers for bass, one pair for mids and highs.The active x-over allowed for gain adjustments for the amps used. And selectible turnover points for the low and high frequencies. Your Denon receiver does not have this capability!

Bi-amping (really bi-wiring without an active crossover) will only work with two identical stereo amps (with equal gain). I don't think it will have any significant advantage over, say, using a pair of mono amps. In your case, with two different amps (with different gain), don't do it! I am unfamiliar with the output connectors on the RTi A7's. Even if they had the requisite two pairs with jumpers, you still cannot connect two dissimilar amps (with different gain) to them!

If the Polks have 2 sets of input terminals, you could try bi-amping them.
You'll need additional interconnects. Not sure it’s worth doing but if you want to play...

You may use a receiver as a pre if it has line level outputs.
Under no circumstances should you hook up two amplifiers to the same speaker at the same time except in the rare case of bridging, which you are not doing.

Each amp has an "opinion" of what the voltage should be and will fight for it. That fight can blow up lots and lots of parts at once.

Best,
E