O.K. I'll take a stab as far as a pre/pro goes over a receiver.

1. Build quality. Decent caps, well dressed chassis (as in how the internal wire connections are routed), external connectors (gold plated vs. not; chassis mounted vs. PCB mounted).

2. Features. Balanced outputs and possibly inputs (for the front channels). Higher-bandwidth component video switching.

3. Isolation. Without high-level amps in the chassis with the low-level preamp, you get far less cross-channel distortion.

4. Amplification. Receivers tend to have lousy amps for the surround channels, concentrating on left, centre, and right. It is recommended that the same headroom be available for all channels.

While I won't argue that one can't tell quality amps apart (though I have my favorites, and settle on $500 a chanel as tolerable, pricewise), double blind, just about any separate amp will be better than the amplification available in a receiver.

Your choice to go with a receiver and separate amps for the channels that matter is a wise one, though, if the receiver is really good, you might find it is the surround channels that are lacking, and not the front ones. BTW, I am not impressed with the M200's specs, esp. above 10 KHz.