Audio research m300

I used to own a pair of M300s.  While they were excellent amplifiers (pretty neutral, though with the 6550 tubes they were a little dry/lean in terms of tonal balance), I don't think they will drive your Thiels any better than the Krell, and might actually have less power into them, given the Krell's ability to double its power into low impedance loads (the ARC is 300 watts into 4 and 8 ohms).  I think for more volume you should consider an active preamplifier, my bet is that's where you'd get more volume.  See if you can borrow one to find out if that's the case.

Yes, I know, but with the ARC the power is the same from all taps, unlike the Krell, which doubles its rated output as impedance halves.

I still say try an active preamp if you need more volume.  Your Krell puts out plenty of juice that should be able to drive your speaker to high volume levels, but your use of the Wadia volume control does limit the gain you can put into the Krell.  This may be one of those situations where adding another component in the chain might offset the more direct route of going from the CD player to the amp.