SET's and solid state

It could sound good. It depends on how sensitive you are to hearing transistors in the signal path. If that doesn't bother you, then it will be fine. Should be no problem with impedance matching. I can't comment on any specific synergy between those products.

I believe that if the GFP 750 is used in its passive mode, there are no transistors in the signal path to color the sound. And if you need the additional gain of the active stage it really doesn't suffer very much in comparison to the purist passive mode. But I believe the unit is very vibration sensitive, so using some proper isolation feet and a good sturdy platform can have positive benefits -- especially in the active mode...

unless your sure your speakers are a great match (not good but great) you're not going to be happy with the s.e.t. using a passive mode preamp will only compound the problem...what are your speakers?