Seeking Advice on NOS DAC

Stretch your budget just a little for a used Pavane. You can later upgrade if you feel the need.  The base model is much better than the Hex and their Level 3 (run through a very good preamp) beat their highly rated Adagio head-to-head, for my tastes, in my system - although the Adagio was very good and other listeners may have called it differently.

FWIW, when I sent my Pavane over to the Netherlands for the upgrade, I purchased an Ayre Acoustics QB-9 DSD because I wanted music and because I always wanted to try one.  It was a nice sounding DAC but IMO and based on my recollection, I would have taken the Hex if I were offered the choice of either.  With respect to full disclosure, I have never warmed up to Ayre's house sound and of the several Ayre pieces I have owned, all have been well-built and very clean and quiet sounding, but I ultimately replaced all of them with pieces I found to be more tonally dense and organic sounding. And the other side of that coin, I have owned 3 Metrum DACs.
Back to the Hex, with the highest respect to Eddie Albert, Eva Gabor and Arnold Ziffel, I find the difference between Hex and Pavane to be much greater than reported by acresverde, but that is my opinion of what I hear in my system.  The upgrade to Level 3 brings another level of clarity and spatial believability.
And finally, if I were in your shoes, I would be looking hard at the Onyx or, if I wanted to ditch my preamp and simplify my system, then the Jade.  Both use the new designed in-house Metrum Transient converter chips that are used in the upgraded Pavane and in the Adagio.
Good luck.

I believe your 1V input sensitivity means your amp/amps achieve full output power with a 1V input.  This is relatively low and should work with about any DAC.  To me, the bigger issue is matching impedance if you are adjusting volume with a passive device.  This can be a significant issue and is probably why I am an advocate of preamps, even though mine is adjusted for unity gain (and buffered).
For example, the Jade and the Adagio (both with onboard volume adjustment) output 2V single-ended (rca) and 4V balanced (XLR) with the volume control handled by adjusting the reference voltage, which does not affect the signal.  Only a few high-end manufacturers (I can only think of Metrum and Empirical Audio right now) offer this type of volume adjustment when going sans-preamp - directly from DAC to amplifier. 
How do you adjust your volume if your DAC directly feeds your tube amp?