[bart]

I'm only able to give you a partial answer.
For movies and multi-channel music I use the Marantz as pre/pro.
My Halgorythme amps do the amplification work.
The stereo preamp has a bypass function.
Sometimes I listen in Pure Direct Mode, sometimes in Auto Mode (with Audyssey MultEQ XT32 room correction).
I listen in 5.0 about 25% of my listening time.

For stereo, my Halgorythme preamp and my mono blocks do a terrific job.
It is still a notch above the multi-channel quality in my system.
Logical, because most of the music I love doesn't exist in surround.

The flavour of my stereo preamp is a little bit different from the Marantz (more detail although it is a tube device!).
But I don't mind.
For rock, I sometimes use the Marantz as pre, because the room correction gives me 2 dB more bass.