I used to have the SH-AC500D and I contemplating buying another (don't ask - long, stupid and expensive story...)
The decoder only pushes out a certain amount of (low) level voltage. You may find certain poweramps that lack sufficient gain or lack level control won't take the fairly weak signal of the 500D. I used to have it matched up to a Marantz THX receiver and there was plenty of volume.
You'll have to get one and test it on your amps.
I have a Parasound THX multichannel now that has level control (ie. volume knobs for every channel) and I think this is what you're after.
I have the Sony 9000es now.
Assuming you have a completely digital setup - the SH-AC500D can work for you.
T.