Tube Pre-amp Suggestions.

I guess it depends on your objectives Solid state or Tube based pre. I suppose your BHK offers a little insight into tube pre amps. I use a EamAR Yoshino 912 which is fully balanced All transformer coupled and has an absolute pearl of a phono stage.You could also consider the EAR 868L or PL if you want an excellent configurable MC  capable phono stage.

To all the respondents recommending and/or using 6SN7 based vacuum tube preamplifiers:  try a set of Sylvania triangle plate 6SN7’s made in the late 1940’s and early 50’s. Something special, and in my experience, low microphonics (not always a given in octal base small signal tubes).

My recommendation would be the Luxman CL-38uC if you’re seeking a full featured tube preamplifier with bulletproof built quality and stunning retro looks.  Transformer enabled balanced in’s and outs, a great phono stage with SUT coupled MC inputs, mono switch, variable turnover tone controls that can be bypassed, and a basic remote.  I know it’s out of your budget, but considering what it includes, the Luxman CL-38uC is a great value sez Art Dudley in his Stereophile review.

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.