Keep B&K 507 or Onkyo NR905 OLD receiver advice

If you love the B&K sound, one thought is to buy one of the B&K multi-channel amps and use the "pre-outs" on your Onkyo receiver.  There's a 7-channel 200.7 on audiogon for $1199.  There is also a 5-channel 200.5 on ebay for $875.  Just be aware that these amps are on the older side -- maybe something like 15 years old (like your 507 receiver).  You could probably then sell your 507 receiver for something like $500-700.  There are probably other warm sounding amps available (maybe like NAD).

This could allow you to transition to a home theater processor, maybe something like Marantz AV7702 (less than $1,000).  Then sell your Onkyo?

Up to you.  It all depends on your budget.

I didn’t mean to dis your Onkyo receiver. I know that Onkyo is very nice for a receiver and your model is VERY hefty at 54 lbs. (hardly any receiver has that much weight). This is very good for its power supply. I was just trying to read into what you like as far as sound goes. The B&K is going to be very warm/rich sounding (I used to own a B&K 200.5 amp). It was too warm for my taste, but others love it. The Onkyo, on the other hand, is going to be a very clean/clear sounding unit in comparison. It is two different sonic signatures. If you like the Onkyo, by all means try it out and see how it goes. The power supply is extremely large for a receiver. It may have no problem driving the 4 ohm speakers.

That being said, if a speaker is rated at 4 ohms (even some 8 ohm speakers), the actual impedance can drop down to 2-3 ohms in the bass/midbass area. Some amps just do not have a large enough power supply to provide enough current for these impedances. The result is weak bass/midbass.

If you feel that the Onkyo is not driving the speakers well enough or if you want the warmer sound of the B&K, then the B&K amps I suggested would be a good solution. They have a very large power supply for just the 5 or 7 channels (I think they come in at about 63 lbs or something). If you decide to sell the 507, you could fund the purchase of a separate amp.

This amp originally retailed for $2495, and based on other older Class D amps, the used price is about right.  That being said, here's a review:

https://www.soundandvision.com/content/rotel-rmb-1077-amplifier

This is one of the First Generation Class D amps.  Back then, there was ICEpower and Hypex class d technologies.  Both had problems and the frequency response had a tendency to be driven by the speaker's impedance curve.  This could result in weak bass, uneven frequency response, rolled off highs.  I owned a set of Channel Island amps, which were of the Hypex module.  They were very nice, but they did not react the same with each speaker.   In the end, I sold them because a high current Class AB amp just sounded better.  Hopefully, the following links come across:

http://www.diyaudio.com/forums/class-d/191597-hypex-vs-icepower-vs-tripath-compare-contrast.html

http://audiokarma.org/forums/index.php?threads/hypex-ucd-vs-icepower.439861/

The new ncore Class D solves a lot of problems with speaker impedance.  However, I have found I just do not like the Class D sound.  I have heard a few newer Class D and they are extremely clean amps.  The problem is they are so clean that it is almost too clean.  They did not have that "organic" feel and did not reach out and grab me.  Not emotionally engaging.  The one ncore option that I would consider (of I was looking at all) is the Nord "One Up" model, which uses a Class A input buffer to help shape the sound.  The Nord "One Up" stereo version is going to be about $2,000 US shipped.  Please be aware that the Nord multi-channel amps do not have this Class A input stage.

These are my own opinions that I have formed.  There are many others that love the Class D amps.

Also I dont want to have to turn on the receiver to watch TV. If all my hdmi signals are going through the Onkyo does it have to be on to watch basic TV?

If you hook all your sources (bluray, satellite, etc.) up to the Onkyo first, then yes the Onkyo has to be powered on to be able see them on the TV.

However, if you wanted, you could hook up all your HDMI sources directly to the TV and then use the digital optical output of the TV to send the audio to your Onkyo.  Heck, you could do this same thing using the B&K 507.  This way, the Onkyo or 507 does not have to be powered on to watch TV.  However, you will have degraded sound quality when watching bluray audio as anything on the digital optical output is down-converted to "old-school" dolby digital or DTS.  You will NOT be able to truly play the hi-res bluray audio formats (such as TrueHD or DTA-HD MA).  Satellite broadcast is usually highly compressed dolby digital, so it won't matter much there.  Another thing to think about is the "digital optical" interface is not going to sound as good as a "digital coax" or even an HDMI interface.