Most Audio Research components today are fully balanced. This was not always the case in the past. You can use a converter and I thin there would be minimal impact. I have a pair of little Canare ends that convert from balanced to single ended somewhere. I have used them in a pinch. But if you later upgraded to a fully balanced preamp such as a Ref 3 or Ref 5se, It will have a positive affect. There is a synergy with both an Audio Research amp and preamp. Even older Audio Research Ref preamps are truly excellent.
I would come up with a long term plan and work toward it. You can have excellent sounding components but if they don't work well together the system won't sound great. Synergy between components is very important. The Sonus Faber Olympica III are very musical speakers. The better the the electronics that feed them, the better they will sound.