Big Red Machine, I'll add my 2 cents in, I've used a few of the amps you're looking at with my X5s. I had a Pass INT-30A I used with my X5s when I first got them, and then I replaced that with a pair of Cherry DTM monoblocks (for sale actually). If you're familiar with the sound of those class A Pass amps, the Cherries are a pretty good substitute, especially for class D. I find the Cherries get close enough to the smoothness of the Pass, but with a crispness to the sound that the Pass lacks.
I also have a few tube amps on hand that I use regularly. Overall, If I were forced to live with just one amp paired with the Spatials, I'd choose to keep a tube amp, maybe my Eaton 45. Even though it only has 2-3wpc, it's by far the best match to these speakers that I've heard so far, even at higher volumes.