DCS puccini+clock or spectral 4000

The Puccini is a sweet sounding unit but personally I would balk at the price. I don't think you need to spend that much for really good digital.

Mechans,

I've found the mhdt Paradisea tube DAC, which uses a single tube in the output stage I believe, changes sound very dramatically with different tubes. I've heard this specifically using a NOS Tung Sol tube in place of the stock GE tube. The difference is at least as pronounced in my system as any other component or cable change I have tried.

I have no experience rolling tubes in other devices though. I have no inclination to date to try it with the ARC sp16 tube pre in my system, which uses 6 tubes total and I suspect is quite a bit more complex to tune this way.