It's a hit and miss thing when it comes to choosing the right speakers based on reviews and advice on the forums. Sorry to hear that the 40.1's did not work out for you. One point to note is the Classe are smooth amps. I don't know about the Delta series but having owned the CAP-100 and listened to the Classe separates I have a general idea of how Classe sounds like. When matched with the equally warm and smooth Harbeth it can be too much of a good thing -smooth, flat, uninvolving and lacking in dynamics. An amp change will improve things, and the real question is whether the degree of improvement is significant enough to transform the whole presentation of the 40.1s, or the difference is subtle at best. That only the listener can answer for himself.
If you want the Harbeths to rock and boogie, Naim amps will provide that edge, and I have tried half a dozen amps. If the 40.1's still fail to rock and boogie with the Naims then the Harbeths are not the speaker for you and remain as a pregnant girlfriend.
A friend of mine, a 40.1 owner who tried a plethora of amps on the speakers(Leben CS600, LFD LEIII, Pathos Logos, Rega Elicit, Sansui, Hungarian-made tube amp and a couple more) also had the same predicament. He couldn't enjoy his music from the 40.1's with these amps as music lacked sparkle and life. He now owns the Naim 32.5 with Avondale boards and 135 amps and is now keeping the speakers. Having said that there also few Harbeth users who changed to other speakers despite using Naim amps on them.
If you want to salvage the 40.1s you might want to consider the Naims. Judging from your response above I think it is a safer bet that you sell them. The 40.1's will not sound like your previous Avalon Eclipse even when driven by the Naim.
Shadorne made a good point. The Compact 7ES3 may be the most successful speaker in the Harbeth line that is quite versatile across a wide genre of music.