I changed up my amplification for my D-40r speakers and I am now using a pair of Luxman MB-3045 factory modified to use 6550 tubes, coupled with a Luxman CL-35 III or a new production CL-38uC.
The best combination I have heard so far in my limited experience. I have not tried a SET amp yet, but will let you know my thoughts if I try one.
Best Regards,
Jim Perry