Impressions so far: line out to external amp is preferable to the headphone out, at least with my Massdrop 58X. Internal headamp is smooth and non-offensive but kind of flat. Presentation using either output is fuller and smoother than the typical budget ESS dac. Most importantly this is the least amount of digititis I've heard in a stock budget stock ESS dac. I could easily live with this as a permanent usb dac. Trade-off is possibly some micro-detail loss compared to previous dacs. Coax update still to come, and then comparison with my own diy/modded cheap but cheerful dac.
Edit: I switched out the 58X for Senn 599s. The 58X are relatively new to me, whereas I've had the 599s for a while now and they're what I used for my dac comparisons the last few years. With the 599s back in the mix I gotta say I am *really* impressed with this dac. They have never sounded this good. Solid, punchy bass, clear mids and even the somewhat less refined highs (compared to the 58X) are clean.
I anticipate any measurement of this DAC to show a very low noise floor.
For the record, previously owned dacs include (but not limited to): Topping D50, SMSL SU-8, Hifimediy ES9038Pro, Sabaj Da3, IFI iDAC 2, Signtek, Fiio D3 (modded), Dragonfly Red, ODAC.