Hi Ed, welcome.
Unfortunately there's no simple way to do what you're asking. In stereo, it might be possible to use line outs from your receiver, and control the volume with the amp input level controls, but this is just a giant pain for many obvious reasons. With multichannel, it isn't even worth considering.
The only way to retain the normal volume control & other functions on a receiver without preamp outputs would be to use an accessory from the car stereo world - a speaker-level to line-level adaptor, connected to the speaker outputs on your receiver. Like this for example:
Axxess ALOC80A Speaker-to-Line Level Adaptor at Parts Express
I haven't actually used one of these with a home stereo, but it should work. A couple of notes:
1) This is not an ideal solution either, since any noise or distortion from your receiver's power amp & speaker outputs will be passed along to the external power amp(s). But this may not be as big a deal as it sounds. Since your receiver's amp/speaker outputs won't be required to supply much current to the adapter (much less than an actual speaker load), they will probably run a bit cleaner in this setup.
2) You probably want to look for an adapter with a high power rating, since these adapters are likely rated for 4 ohm inputs - 4 ohm ratings are more common in car audio. Most home receivers are designed for use into 6-8 ohm loads, which is a higher output
voltage. A higher power rating on the adapter should buy you some more headroom for dealing with this difference.
3) You might want to start out with a single stereo adapter and listen to 2-channel stuff through your bigger amps, to see how it sounds. If it works OK, then go back and get more adapters for additional channels if needed.
Good luck, and let us know how it goes.