Other then photo inputs which can be solved with this http://www.amazon.com/Parasound-Zphono-Phono-Pre-Amplifier/dp/B001KALK4Y
What are you looking to improve?
Marantz makes a great processor and there are a lot of choices for amps...
If you bi amp, use two channels instead of one, yes, your delivering double the power, and that should add 3db more volume.
If the speakers allow for it, it is likely there will be sonic improvements from bi amping, or bi wiring the...
Ithink the NAD amp will improve sound. More power, more control, more headroom all helps. Plus when you use a receiver, your dealing with many compromises to fit the amps and processing in the same housing, all using the same power...
I think just about any seperate amp will be more powerful then the receiver. I compared the built in amps (110x7) in my Pioneer Elite VSX-32 to an external Parasound HCA-855a (85x5) and the Parasound would deliver about 5 db more clean...
Just about any mid range reciever will fit the bill. I recently picked up a Pioneer VSX-32 for $399 and it's working great. Look for features more then power. Power ratings on receivers are for the most part, useless. Technically...