best amps new and used for Infinity RSIIb speakers

ARC VT-100 (I have the Mk. 2) is magical with the RS-1bs: liquid, huge, airy soundstage. They were originally designed with Conrad Johnson tube gear, BTW.

I owned a pair of RS2Bs for several years. You definitely need to use tubes. CJ or ARC would be ideal -- even some of their older stuff. I also owned a Music Reference RM9 II and that was very good as well. The more power the better but 100 or 125wpc will do fine. Good luck.