A tube DAC with volume control, suggestions ?

Save some cash. mhdt Pagoda + a TVC (transformer volume control). Resolution & tone. The Pagoda isn't strictly a "tube dac." It has a tube output buffer connected to an R2R organic DAC with a discrete transistor DA stage prior to the buffer. It sounds sublime, up to 24/192. Strap a TVC to it and settle in for organic realism.

Phil

Audio Research Reference DAC / Media Bridge

If you desire the best  possible sound quality look at Lampizator.My friend is using it in his system and it was a big sonic upgrade.

Audio Research has one called DSPre there is one on Audiogon for $2700 new list is $7500 i believe it is a current model 
that is all i know about it