I have to disagree with the other posters on the speakers. I think the Rotel/Krell combo is causing the harshness you are hearing. I am very familiar with the ADS sound since I have a pair of L1290s I bought in 1984. As you are probably aware, they have the same midrange and tweeter that the L1590s have and, if anything, are on the warm side of neutral. I no longer use them in my main system, having upgraded to Soliloquy 6.5s last December, but I used them for 17 years, finding it very hard to find something significantly better. The L1290 and L1590 are still very competitive with modern speakers. In my own search, I couldn't find anything under $4K that would beat them. The Vienna Beethovens sound very similar to the L1290s.
You said they sound best at higher levels which sounds strange to me. I found the L1290s to sound more realistic at low levels than most other speakers. This makes me think you have a component (or cable) that is compressing dynamics.
See if you can borrow a top-flight SS amp (Rowland, Pass, Levinson) and some good cables (Cardas Neutral Ref. or Kimber Select) before you give up on the ADS's.
Another thing, I'm pretty sure your speakers are not meant to be bi-wired. The two sets of binding post are meant to be used with an active crossover. If you try to feed full-range power to the tweeter I think you'll damage it. Maybe this is the cause of your problems.