Interested in hearing about tube rolling experiences with the Orchid and other MHDT dacs, namely, the specific comparative sonic characteristics of the various 396a, 5670 and other compatible tubes used in the output buffer. My only experience is with the WE396a that Linear Tube Audio installed in my new Orchid.
the reason I like CBS 2C51
3D soundstage, Real representation of recording with nothing over-emphasized.
e.g Prominant attributes were emphasized (voice, piano in Behtoven's 5th piano version)
The other parts of the music were in background....but the details were still there.....u didnt miss much if any.
Instrument separation & clarity of instruments in busy music made it easy to listen & enjoy.
AND Not Bright at all
The emotion in the vocals were present, because even if small amount of decay/breath or Ahh (they were there in just that small amount)
FOr other tubes...which I call not emotional....these were missing.
My system
Custom PC -  MHDT Orchid - Luxman R117 - KEF 107/2

I have had experiences of using Vintage E88CC and have been demonstrated some of the Valves mentioned above in devices that I own.

As a result I have acquired a selection of early 60's E88CC's from different producers

One Tube not mentioned and very worthy of being trialed is the early 60's Mullard CV 2493, these are rare to find, even thought not too long ago there was a Matched Pair for sale in the USA, for very fair money, if compared to present UK prices.

I also recently heard on two separate occasions an early 60's German produced E88CC in a CDP and the impact it had made on the device and within the HiFi system was extremely impressive .

The second listening was with a Group of attendees who had at an earlier date, been demonstrated the CDP with the stock valves. The response from the additional attendees were no different to my own, they were in awe of the presentation on offer, and very clear about the valuable impression being made in their appraisals. 

I just want to say thanks to jjss49 for helping me find the right mix of tubes for my Istanbul and Blue Circle pre. His assessment of the REFLECTOR 6H23P-EB / 6922 (PREMIUM) was spot on and switching back to Amperex made all the difference. Great to have some solid advice from someone who's listened to a number of the different options. Saved me a ton of angst and painful discovery.