Will the Audio Research VT-50 drive the 1.7's?
Marginal. You'd have to try it because it's going to depend heavily on how loud you listen and how far you are from the speakers. You used to hear a lot of D-76's on Maggies and they sounded great. But in my experience and that of many others, they benefit from more oomph. (To put it in perspective, you'd need 1000 watts of solid state amplification per channel to subjectively double the maximum loudness of the VT-50.)
Anyone know if the NAD 375BEE can, with all it's power supply and circuit machinations, drive the Maggie 1.7's in a medium sized room?
Sad to say, there's no way to answer that since it depends on the level at which you prefer to listen and the type of music you enjoy. *Can* drive, no question about that, it isn't going to blow up and it will get pretty loud. But those who like to listen at high levels will generally notice Maggies "coming to life" with a larger amp. This is a function of peak headroom rather than RMS levels, which in this case are sufficient to blow the speaker fuses.
Try a used VT-100!
How about a Rotel RB-1572? 500W / channel at the Magnepan 1.7's 4 ohm rating (250W @ 8 ohms / channel). Class D, however, and afficionados prefer the previous models. Or the nice Cambridge Audio 840W class XD (better AB?) amp @ 350W @ 4 ohms (only 200W at 8 ohms per channel).
I can see your attraction to Audio Research, however.
The VSI 60 (VT 50 replacement?) looks buyable, and almost scientific in appearance! :)