Personal recommendation: the Aune X1s is still a fine unit, and while the 10th Anniversary Edition has a more powerful amp, the dac inside is just "okay" imo.
If you're looking for something in that same price though, you could also go for an OL DAC from JDS Labs and an O2 Amp from Massdrop. That's roughly 200 bucks and people have said the O2 pairs well with the 6XX.
Alternatively, the SMSL M6 is a fine option for an p/Dac, while the amp section isn't super powerful, line OR pre-outs for powered monitors and digital volume control with a remote is a definite plus. I've run the 6XX off the older M6 and it's still a fine experience.
Actually just tested them last night with the Aune X7s being fed from the M6, and... Well I didn't really like it. I preferred the 58X being fed from that chain. But yeah, you can't go wrong with the newest M6, the JDS Labs OL DAC + O2 Combo, the Aune X1s (though I think the dac could be better, it's a very subtle thing to my ears), or if you wanna ball out, go for the Schiit Jotunheim with the Balanced or Multibit Dac.
That or the NFB11, R2R11 are going to offer some good power and room to grow. That's my opinion anyways. Good luck tho meng!