I'd use fairly clean guitar sounds through tube amps if you have them. Some of the Floyd stuff is a mix of direct and mic'd amps, with the mic'd amp having a lot of added hall type reverb.
The bass sounds on a lot of prog. stuff (like King Crimson) is nice and chunky, like maybe through a 15" speaker and driven pretty hard. The entire second side of the Red album by King Crimson has this kind of bass.
The drums always sound pretty loose, maybe only 3-4 mics. The snare is usually kind of distant, but crisp. I'd definitely stay away from samples and rely mostly on overheads. Just keep trying different drum mic configurations, with a limited number of mics, until you find one that you like. The kick punches, but doesn't have the kick you in the chest bassy, woofy sound. You just might have trouble getting the right sound you want without the aid of tape compression.
Without getting too fancy, I'd say those are the basics! You have to watch your levels with synths going into analog equipment because of the transients and such, so I'd watch them even closer since you're recording to digital. I doubt you'll get the exact sound you're trying to recreate, but you may get some newer, different ones that you may like. If that's the case, you may want to try using a few digital effects they didn't have easily available at the time, like reverse delay and such. Just remember that the progressive rock era was all about experimentation, doing unique stuff, and using the equipment that was available at the time. If you keep that in mind, and try to create prog. rock without too much imitation - then voilla - you've got prog. rock.
-MD
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