Alex I think you just had a contradiction in terms.
The only compromise I made was using the XDS1 with an Audio Research Ref5SE tube preamp to get the extension and midrange/soundstage
Well, with 150 Ohm unbalanced or 300 Ohm balanced, the XDS1 can drive any preamp or a power amp to the moon. This said, introducing the AR Ref5SE to your setup, in my opinion, gives a coloration that is not only suitable for your taste but also being synergistic to your audio system.
So yes, while the tube preamp can provide the "missing link", it is something that "compensates" for your source, meaning, your source has a tad more to be wished for - in your case the AR preamp.
Above said, there is no contradiction. :-)
Best wishes,
Alex Peychev