What do you want to improve from the CXA81? I own that amplifier and I give it the highest praise possible at its price especially when paired with the LS50 OG or Metas.
I tested the Metas extensively woth several amplifiers, including the MF M5si. That thing is a monster and sounds so strong, but neither of us testing liked it very much with the Metas. It sounded strong and with some songs interesting but it wasnt as good as sone of the other amps we tried. In fact, it was the second worse pairing only behind the Monoprice Monolith.
The best one by a wide margin? Peachtree AMp500. Second best was the Emotiva XPA gen3, then the CXA81, followed by a smaller Emotiva that I think it’s now discontinued. They were all tested with several DACS and we all preferred the SMSL M400.
BTW, if you manage to get a recertified AMP500 (mine was 1000usd two years ago) I am sure it will sound much better with a 300usd DAC than the CXA81 for the same price.
I hope this helps, OP.