FWIW, I have used a Classe Audio DR-15 with my Sonus Faber Electa Amator speakers for the past twenty years, and I’m still happy with the results. I can’t comment on the effect of the 4 ft knee walls (or even what they are-LOL) but I’m certain that the above recommendations for Thiel, Spendor and Vandersteen speakers are good ones.
