I'll chime in:
1. Isolation does make a difference with this DAC. I use a K-Works IsobaseK, and prior to that a Seismic Sink. Both made a big difference, as noted above.
2. For tubes, I agree in the units without the transformer upgrade, the 12AU7s have the biggest effect on the sound. I've always been a Telefunken fan, and I used both Tele 12AU7s and ECC802s in there. The Teles probably are a little rich around 200hz or so, because after I got the transformer upgrade I could hear a slight dip at that crossover frequency in my speaker system, where the satellites pass over to the woofers (fixed that with a phase control). Jerry used to use Mullards in there, which I found lively but with just a little too much glare for me. For the 6922s/6DJ8s, I've settled on Siemens, both Ccas and ECC88s as my tubes of choice. The Sovteks are OK, but not in the same league. I've also heard people claim the NOS Sylvanias work well in this DAC; perhaps if Joe Kubala is around he'll elaborate.
1. Isolation does make a difference with this DAC. I use a K-Works IsobaseK, and prior to that a Seismic Sink. Both made a big difference, as noted above.
2. For tubes, I agree in the units without the transformer upgrade, the 12AU7s have the biggest effect on the sound. I've always been a Telefunken fan, and I used both Tele 12AU7s and ECC802s in there. The Teles probably are a little rich around 200hz or so, because after I got the transformer upgrade I could hear a slight dip at that crossover frequency in my speaker system, where the satellites pass over to the woofers (fixed that with a phase control). Jerry used to use Mullards in there, which I found lively but with just a little too much glare for me. For the 6922s/6DJ8s, I've settled on Siemens, both Ccas and ECC88s as my tubes of choice. The Sovteks are OK, but not in the same league. I've also heard people claim the NOS Sylvanias work well in this DAC; perhaps if Joe Kubala is around he'll elaborate.