IMHO, based on my limited experience, the pre amp plays a more influential role in SQ than the amp in a separates-based system.
I would personally shy away from a

Adcoms hold up like a steel brick. That being said, I agree with wkhanna that a good preamp (like the Adcom GFP-750, no longer available new) makes a huge difference to the sound you'll get. Hard to predict whether you'll be better off with one strategy or another in the used market. But if buying separates seems like more fun and you're figuring that you'll eventually upgrade, enjoy yourself.