Apogee Acoustics Caliper,which amp?

I'm really not a Krell lover, but I have to admit that a KSA300 is probably the best amp for these (or any other non-hybrid) Apogees. Don't like the Krells with other speakers I've owned or heard, but they do sound pretty good with Apogees. Good luck -- nice classic speaker -- replacement ribbons are now available from a chap in Australia. Check out the Apogee newsgroup. Good resource for owners of "orphan" speakers.

Forgot about an amp that should work very well with the Calipers (or any other non-hybrid Apogee). Check out the Innersound amp. This was designed to power their own esl's. Unlimited headroom, loads of current and voltage. All the things that your speakers need. Supposed to sound quite musical, to boot. Innersound has a site with info about their products.