Agree with the power cord comment, but my guess is that you are already using a good cord. If you haven't tried a different/better cord - say a good Shunyata helix or equivalent - you might go there first to see what that does to smooth out the higher registers on the 9100.
The Harbeth is not that sensitive, but also not rated for massive power either. The tube idea is a good one if you crave warmth and "continuousness", but to get the kind of authority you need for quality classical and rock reproduction, I think you generally would need to go to with tube separates. How about a hybrid?
I have read but not heard that the 9200 is brighter and more forward than the 9100 (maybe more Krell-like?). Focusing on the middle to upper end of the recommended power range, I would look at these excellent integrated amps:
1. Bryston B100-SST
2. Creek Destiny
3. Musical Fidelity A5.5 or A1008
4. NAD M3 Dual Mono
5. Naim Nait XS or Supernait (lower advertised power, but Naim sound)
6. Vincent Audio SV-236 MKII Hybrid