I haven't offered the pre for sale as the costs are pretty high. I'm very happy with the performance though, it's an amazing sounding preamp.
I'm not sure the tube buffer or any tube preamp is going to be a good idea with a Lampi DAC with DHT output tubes, but it's hard to say... the buffer has an output impedance less than the Lampi, about 500 ohms where the Lampi is going to depend on plate resistance of the tube in use, but that'll always be a good bit more than a cathode follower buffer. I'm more thinking in terms of tone, which is a good part of the appeal of the Lampi DACs having that DHT output section. You might want to consider trying the Lampi without a pre or just a passive pre like the Tortuga, my guess is it will be better overall that way. In my system I prefer the buffer over the Tortuga straight, but the tube output section does add a tiny bit of noise... moreso than a preamp with gain as the signal isn't amplified, it's actually reduced by 3-4 dB. With the Lampi DAC I can't see the additional noise and complexity of a tube buffer being worthwhile.
On the tubes, the 6922/6DJ8 are great tubes as well. The circuit design and parts quality will make a much bigger difference than 6922 vs 6SN7. The tube buffer I used in my preamp is Broski's ACF circuit, which uses a triode as a plate load and has a bipolar power supply to cancel some of the PS noise at the output. It's a very low distortion circuit that does not sound tubey at all, you get some of the 6SN7 sound from the buffer but not too much "tubiness".
Thanks Dave. I believe the dht tubes are on the L7 version and up if I remember right. I have a L4 with 12au7 and 12at7 tubes. I had tried a Tortuga pre a while back when I was using a dspeaker am 2.0 as a dac and thought it was ok but the Rogue Perseus I had at the time had more detail and better sound stage which was the opposite of another forum member here who used to have a Perseus before he got a Tortuga. But he was using a Eastern Electric dac in front of the Tortuga.
I think Morten might have another tour coming up so I may get another chance to see how it goes. I feel at this point I'm just tinkering as what I got now really sounds phenomenal. I guess it's a case of always wondering "hey, what if...."