Tube for aesthetix pandora / romulus


I own an aesthetix pandora dac and i am thinking of upgrading its tubes:
- 2 E83CCS or 12AX7
- 2 6922 (6DJ8)

I have been advised to get mullard, siemens or telefunken nos valves

I don't know anything about tubes...

Would you have recommendation? Advises? Tips? Good tubes sellers?

Thanks and regards
A no brainer choice would be Phillips (Haarleen plant) ECC83--ie 12ax7 European equivalent. Look for the Delta codes from the early 1960s. Google and you will find all the background you need to know. They will beat the Mullards. Thank me later.
And these will lower the noise floor? What other benefits have you heard? I won't become obsessed, however I may be willing to experiment a bit. Thanks
I use matched Gold Lions from Jim McShane in my Pandora Signature(currently listed for sale).
I tried Amperex ECC83 Holland tubes from the 50's (Haarleen plant) and did not like them in the Aesthetix. I don't see how phillips would be better.
Dont knock em till you try them. Phillips Delta codes 1960 and up to about 69.