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.

They have speaker terminals on the back for 8,4,2,&1 ohm loads. Thank you for the reply. 

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.