How big is your room and how far from the speakers do you normally listen ? The Ohms seem like pretty good speakers both in terms of reputation and ability to move air, so going to a significantly smaller speaker might not work for your room if you like to play at louder levels.

I'm a big fan of M3s; only caution is that they may not play as loudly as your C2s.

For anyone who tried to look up the C2 and didn't find much, here's a link to the mfg site. To their credit they still offer replacement drivers 30 years after they sold the speaker.

http://www.ohmspeaker.com/store_item_detail.cfm?item_ID=7&cart_ID=11189315876

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8