Rowland 8ti or Krell FPB600c

You have one of the best power amplifiers that money can buy. The new Jeff Rowland Model Nine’s are a consideration as well. You might consider looking for the upgrade you seek in other components in your system. Cables, Signal source D/A (if you use one). These are all places your overall sound may fall short of the full potential of your power amp. I would suggest you do a detailed evaluation of your current sound, focusing on what you hear rather than just one component. After that decide what you like or want it to sound like. Then experiment with different components other than the power amp that will effect the overall sound. Every component in the signal path will affect what you hear. You didn’t mention the other components in your system. I think after a close evaluation you will find the overall sound is the sum total of all the components. It would be all but impossible to orchestrate the overall sound by focusing on just one part of the system. Much like a symphony the conductor directs the entire orchestra not just one section. The old saying a chain is as strong as its weakest link. This is worth considering! Good Luck