I'm not sure if it will work the same way in your system, but I got great results using a Monarchy Audio M24 tube DAC/linestage with the TAD-60. To me, the Monarchy sounded a little more "right" than the TAD-150 Signature preamp, but I didn't do any tube rolling with the TAD-150.
The Monarchy M24 sounds very good with its stock 6DJ8 tubes, but I put some Siemens E88CC gold-pin tubes in the DAC stage, which made the sound a bit sweeter and more liquid. You can also run an extra source (like a phono stage) through the M24's tube linestage, and I find that feature very convenient.
I'm still using the stock EL-34 tubes in my TAD-60 and I'm running it in triode mode with just a bit of feedback because my speakers are efficient enough not to lose bass or dynamics that way. And the sound in the midrange is smoother and less etched.
If you look at "My Desert Oasis" system, there is a good pic of the M24 there, which can be made larger. Good luck in finding the type of sound you are looking for.
The Monarchy M24 sounds very good with its stock 6DJ8 tubes, but I put some Siemens E88CC gold-pin tubes in the DAC stage, which made the sound a bit sweeter and more liquid. You can also run an extra source (like a phono stage) through the M24's tube linestage, and I find that feature very convenient.
I'm still using the stock EL-34 tubes in my TAD-60 and I'm running it in triode mode with just a bit of feedback because my speakers are efficient enough not to lose bass or dynamics that way. And the sound in the midrange is smoother and less etched.
If you look at "My Desert Oasis" system, there is a good pic of the M24 there, which can be made larger. Good luck in finding the type of sound you are looking for.