Hi Al,
1) The MS600 performance is noticably better than the MC200, good as the MC200 is.
I think you've covered most of the improvements in your questions!
Think of it as an ID40 card in it's own case.
2)Yes its analogue outputs can be set as fixed, to go into an analogue pre-amp / integrated, or as variable, to drive a power amplifier directly.
The volume is Meridian hybrid analogue/digital like their other products.
A big step up from legacy Ensemble and Source products which I believe were digital only.
Cheers,
Rick