Schiit Freya+(Plus)

With all due respect, I believe your question has been answered above.

Schiit says use matched pair on both gain and output pairs. Others say not necessarily. Just be aware of impedance mismatches. 

Experiment. Rolling is easy with the Freya+. 
You don't need links to retailers. They are named in the posts above and any third grader can find them on a Google search.

My advice, start out with the stock tubes (JJs last I knew), get a good fix on the sound with familiar material, then try Tung-Sols, right then left, then move to GE or whatever. Bad impedance mismatches will probably announce themselves.
BTW, one of the original JJs in my unit went south after a couple weeks. Schiit said move it from buffer to gain, I did, and the defect was no longer noticeable. 
But then soon after, I rolled the whole batch and am still doing so when the urge strikes.

In my experience there is no easier, cheaper preamp to roll tubes on than the Freya+. Seems to be designed for the purpose. So have at it. Read the posts above and remember nobody will have the same experiences given different rooms, different connected equipment, and different musical preferences. There is no magic answer for YOU. Read the tips above and proceed accordingly. You will know it when you find it.
 

ok, let me see if I found the correct pair of Tung Sol 6SN7 for the LEFT side from rhing:

https://www.ebay.com/itm/313513219446?hash=item48fed81576:g:AfUAAOSwZ8ZW~CRx

Here is the pair of OS GE gray plate side getter 6SN7 for the RIGHT side:

https://www.ebay.com/itm/173936316220?hash=item287f698f3c:g:90EAAOSwEFhdlMVU

There are so many Tung Sol tubes and GE tubes. Not to mention some GE tubes are from the 1950. Is everyone using tubes from the 50s or from current years?

Definitely you are overthinking, just as I was doing when I started this thread.

Like your current combo idea. Give it two weeks and see if it leaves you wanting. If you find something missing, then roll, roll, roll. The possibilities are endless and the enjoyment lies more in the process than in the end result -- assuming there could ever be an "end." As ever, it's about the journey, not the destination. 

I like the preamp. I'm happy with the sound. Ditto on the Sylvania GTB. Paid $100 for a NOS pair and they pretty much transformed the preamp. They now come with Electro Harmonics tubes instead of JJ. My only complaint with Schiit equipment is it's built to  price point and the RCA inputs are not as durable if you like to change cables a lot like I do. I've had problems with the RCA inputs coming loose or losing contact. But then look at the price. For a couple hundred more you might like the Vincent 32 model preamp. Personally, I wasn't that happy with the sound of the JJ or the EH tubes. 

Thanks for the report. Never tried the Silvanias myself as there were tales of excessive brightness and impedance troubles. But you never know until you try, and it's not that expensive. Plainly you're right about build quality. My own approach has been to get along with the Freya, which is fun and easy, while upgrading other components, cables, conditioner, then finally decide on my "forever" tube pre. So far, so good, and I'm due for another roll now that the sound of newer gear is stabilizing after burn-in.