Adding a tube DAC to my BLUESOUND VAULT

I recently purchased a used BLUESOUND VAULT ( cd ripper and streamer) and after reading a lot of posts on various sites I may add a Tube DAC in the $500 or less price range to my setup  I have the VAULT hard wired via CAT 6 > RCA out to RCA INPUTS MFA MAGUS A2 tube preamplifier > MEITNER MTR101 MONOBLOCKS > BOZAK URBAN speakers. So, thank all in advance May I have some ideas and suggestions please?
For that low price you will have to buy something made in Ch*na! Which is ok! Look at your smartphone! Guess where that came from!
I think you may need to up your budget to the $1000 or so level and look for a used MHDT Orchid or Audio Mirror Tubadour.  You might also consider a solid state R2R NOS DAC that tend to have a more “analog” type sound, but those too will be tough to find at $500 or less.  Best of luck. 
$500 for a tube DAC, I’d go way back and find a California Audio Labs Alpha if you can find one. That was a nice tube DAC in the day and I bet will still hold it’s own today. The CAL Sigma was the model below and still decent but not as good as the Alpha. 
Other option and new would be the Jolida Glass FX Tube DAC II. I’ve not heard one but Jolida’s always get good reviews.