Tube Pre-amp Suggestions.

A stand alone DAC that also performs the function of a preamp is very unlikely to come even remotely close to the performance of a stand alone preamp. Companies have been founded on building great preamps and the best today are still built on two box designs and cost a fortune. So, an add on function to a DAC is unlikely to perform anywhere near the level of a purpose built preamp. Some very expensive DACs may have serious preamps in them. 

Class D... for instance ADG sound great through for instance an Audio Research DAC. I had a chance to listen to one in my system. Amp technology should have no impact on your preamp... unless it has so very unusual output. I've been mixing and matching for decades and never had an issues... the better the preamp the better to output sound. 

I have a Prima Luna Evo 400 that feeds my  Brysto 4b3 SS amp that I feel really made a big difference in SQ over the SS Parasound pre I had been using. It’s my first tube preamp so I can’t see how necessarily compared to anything else, I got my system to the point where I don’t really have any desire to make any changes and Just want to listen to it as it made all sorts of music more enjoyable. The 400 is over what you want and o spend, but you might want to listen to or consider the 300 or even the 200 which are more reasonably priced.

schiit fot the win.  It goes digital too.  It was my very first. Never forget your first.

@porchlight1 

When you say Sylvania "triangle Plates" I beleive you are referring to the angled T plates in the GTB series? They started in 1954. Not as good as the previous GT series, but still great quality Sylvania tubes.