Jglpubli, first, let's take it a bit further.
Few more questions:
1) is the REF3 broken in? Do you at least have 500 hours of playing time on the unit?
2) REF110 - how many hours? Broken in or not? Should have at least 500 hours and even more to be considered for a serious audition, same as REF3.
3) Have you had the D200 on these speakers or you had other speakers at the time?
If it was with these Proacs, it is pretty much a hint that you may just need more power to balance these speakers out. that's one. Also, D200 does not have the resolution of REF110. You are hearing a lot more imperfection now with the REF110 and REF3(don't know what preamp you used with D200). I'm just going by the fact you used a phrase "some recordings". So that should be considered as well. Let's not forget the high resolution of the ARC REF stuff.
There are few variables. Best is trial and erro as far as equipment for a specific speaker, be it a ProAc, Wilson, B&W or what have you.
If at all possible, borrow a more powerful solid state amplifier to try with your REF3. Try to audition a nice solid state, hybrid(tube/solid state design such as ARC's own HD220 or Moscode) or a more powerful tube amplifier.
You can have the best possible pieces in your audio rack. But if they don't synergize, whatever you have isn't a "system". Yes, good on their own, but not necessarily together.
Also, I very much doubt 100.2 will satisfy you. it is a very good amplifier, but I kind of doubt it will drive the Proacs any better than the REF110 do, especially if the reason for your complaints is due to lack of power. The only thing you may gain with the 100.2 is somewhat more forgiving sound overall, because it won't have the resolution of the REF110. But it will be still lacking.
Try to audition few different amplifiers, possibly more powerful than the REF110. Some to consider would be Classe, Pass, McIntosh, McCormack DNA-500, ARC HD220.
May be I'm wrong(wouldn't be the first time), but it seems to me it is a matter of finding a proper amplification for the speakers. Also, work on the room acoustics if situation allows. Very essential.
