Tube imperfections

I can just about guarantee there are differences you will be able to hear if you listen for them. You will probably also find some that make a big enough difference to be obvious. You might even find one that is so obviously better it was worth the money. But I can also just about guarantee this will not happen on the first try, if ever. Almost always what is much more likely is you will go through three or four modestly different results, just enough to tease into keep trying, maybe after four or five you get one good enough you feel maybe this is all worth it, maybe this next one....after a while it starts to seem you're getting closer and closer wow these tubes really are distinctive. 

When really what is happening is you're getting better and better at the fine art of discerning differences between tubes. So that if one day you do find the white whale it really will feel like a white whale. Even though at the end of the day the difference between the very best and the very worst of them all is less than one $160 Synergistic fuse, only you had to spend five years and $1500 to figure this out. This being more cognitive dissonance than most can stand you inevitably decide it was all totally worth it. And round and round we go.....
Another thing you might learn along the way, which nobody mentions, is instead of tube rolling you could be diode rolling. Because, let me tell you, there are massive differences between diodes. They cost a lot less. Changing them pays bigger rewards by far. And its just about as much of a crap shoot. But it calls for soldering skills. So nobody does it. Otherwise for sure if someone ever invents a diode you can just plug and unplug then by God audiophiles will all be into diode rolling. 

Oh wait- tube diodes! Nevermind! lol!
https://www.youtube.com/watch?v=K0gSNTAA0_Y

I have the mhdt in a second system and find the 6n3 comes across with a nice cleaner sound thank the GE or WE. The strange thing is and I may try it is to get tube adapters ($25 very nice quality) from Garage 1217 web site and run 6922 or 6sn7's. I have a huge stash of very nice NOS 6922, 6sn7 tubes. Check out Head-Fi web sight on preferred tubes for the mhdt. Many run the 6sn7 and 6922 which I would think is a much better tube than the funky 5670 but it does sound good so going with adapter may be a waste of time. I've not heard of mhdt going up in flames using adapters.

MC, thanks for that!  In regards to diodes I shouldn't doubt you but one thing at a time.  I'll stick to a tube or three and just select the "best" given my ears, the way it works in my overall system.  You had to mention the f___ word.  Here we go!

paulcreed, indeed I've picked up on the adapters and the new list of tubes that it opens up.  So far, my first impressions of the 6N3 is similar but to MCs point, different often comes across initially as better but time and repeated A/B will tell.

I would just try the tube and see how it sounds and go from there.
I had a mhdt Paradisea for awhile. The tube used made a big difference in the sound.  The stock GE tube provided was a tad too warm and fuzzy for me.  Not expensive to try different ones and find out which works best for you.  I ended up liking a Tung Sol.   But YMMV. . 

My current DAC is a mhdt Constantine.

For those perhaps curious,  I've listened to the Raytheon JAN 2C51 and the Russian  6N3P-DP each after 24 hrs of break in, in the Orchid DAC.  Compared to the WE396, both had way more clarity and definition.  Both cleaned up a muddled bass IMO.  The 2C51 seemed the brighter.  The WE396 was more akin to the wall-of-sound and the others were more discrete on staging.  Preferred the 6N3P as the 2C51 had a bit too much space between the instruments.  It wasn't hard to tell the WE396 from the others in multiple A/B sessions.  I've got one more to roll in and then head to head it with the 2C51 and 6N3.  The 3 new tubes ended up costing  about 12% of the DAC and was money well spent.  Less than a nice IC with likely way more impact.  I'm using Cardas Golden Presence RCA and a Cardas Lighting 18.