@rivinyl , I am not familiar with the Audio Note Dac 2.1’s sound, but I would be surprised if one found the Aero lean sounding (even with the stock tubes, which are indeed a bit more matter of fact/slightly drier sounding than various NOS tubes I’ve tried out).
You can get a better idea of some listening data points from @mitch2 ’s reporting on here (linked above) and Michael Lavorgna’s reports of result of tube rolling with the Aero, also referred to above by @katzenjammer27 . IIRC, Mitch liked the Aero but preferred several other non-tube DACS over it —and then moved on to the (differently) tubed, legendary Aries Cerat Helene — but never described the Aero’s sound as lean.
Given the Aero’s price and LTA’s try it at home policy, I don’t have any hesitation in recommending that you test out in your space &system and see what you think.
Oh, i should add that LTA says that they think the DAC plays equally well with SPDIF/coax as it does with USB input. And from my 2 systems (one USB and one COAX), I do not disagree. I think it depends on your streamer as to which will sound better in your system. That flexibility is a pretty nice feature, IMHO.

