Moose89,
First congratulations on the pre-amp, that's a great start.
Second 12AU7 type tubes have gotten very expensive of late, my favorite are the Mullard NOS (not new production) or the NOS Amperex versions with gold pins....these will both be around $100 per tube, but are amazing tubes. NOS tubes will definitely give you the "warmth and soundstage" that you were referring to.
A very good 12UA7 tube is the NOS RCA "clear top" tubes which can be found under $40 and will be better than any new tube. Brent Jessee will carry a huge selection of 12AU7/6DJ8/and his reputation is perfect http://www.audiotubes.com/12au7.htm
Third if you do decide to go with a $1,000 DAC, I'd recommend looking at the Denafrips Ares 12th edition at $1,000.....not the Enyo/Ares II version for $870. It's definitely worth the extra $130; and is definitely on the "warmth and soundstage" side....and I'd add "fun" as well.