I have had a number of Class D amps with my Nines, including Red Wine, Bel Canto, and Cherry, but now have the Pass X150.5. The X150.5 was the only amp that filled out the Nines' midbass as well as my tube amps, only with more accuracy and better bass extension and impact. Huge, deep soundstage, quiet, resolute.
Better pairing than with the First Watt J2, which, like the Class D amps mentioned above, sounded thinner than when paired with the X150.5. I'd also try the XA30.5, which John D was interested in checking out with the Nines when I chatted with him earlier this year. I would also like to check it out, but the X1/X150.5 make such beautiful music together I'm not really that motivated TBH.