I had a Phonitor XE with DAC in the house for about a month to do a supplemental review at Basshead.Club.
The short version: The DAC part is very good, but is outclassed by the amp (in that the amp is superlative).
It’s the inverse of the RME ADI-2 DAC, which has an outstanding DAC that outclasses its very good amp.
If you specifically need an all-in-one unit, I would likely go so far as to say that it’s better than the ADI-2 DAC if sound is the only consideration.
The USB is quite capable. I tend to listen for USB issues that I describe as hash or swoosh. Those issues are very common and are present in almost all USB implementations (exceptions include RME, Schiit, and Soekris). The SPL Phonitor XE does not have these issues.
The Uber-DAC is clean, transparent, and revealing. Without an amp as resolving as the Phonitor XE, it would be difficult to tell the difference between it and the RME. For those familiar with the ADI-2 DAC/Pro, I believe the Uber-DAC sounds like it uses the SD Sharp filter.
My only real issue with it is that you’re paying a considerable sum for a DAC that can only be used with one amp. Without preamp outs or direct output from the DAC, the DAC itself has essentially no versatility. You’re locked into the stock filter of the AK4490 and can only use it with the Phonitor XE amp.
For a couple hundred more, I slightly prefer the RME ADI-2 DAC and it comes with incredible versatility (more than any DAC ever, to be fair).
Back to the USB momentarily: I did feel the sonics were improved just a touch by using the AES output of the RME ADI-2 Pro FS vs. the USB of the Phonitor XE. It became more effortless and smooth in comparison.
As an AIO, the Phonitor XE is outstanding, but it’s hard to recommend if you ever plan to have an additional amp.
In the end, my personal setup is an RME ADI-2 Pro FS going to an SPL Phonitor XE without the Uber-DAC.