I started with an MC275 (90 wpc) with my Reference 5s and the sound was good. Very smooth with nice mids and smooth highs. Not the best resolution, but cast a fairly good sound stage.
I moved to Electrocompaniet Nemo monoblocks and the Reference 5s really opened up. The Nemos are on the warm side, so didn't miss any of the wonderful mids and highs that I loved about the MC275. The first thing I noticed was the much faster and very articulate bass. The sound stage became much wider and deeper, with excellent separation.
As I mentioned above, the Reference 5s really like clean, high current power. It will be interesting to get the results of your experiment and see if you can find a great matching amp in your setup.