6DJ8 vs. 6922?

I just switched a 2c51 tube in my MHDT DAC with a 6922 with adapter better bass and bigger soundstage

Every piece of gear that I have owned that uses 6DJ8 tubes, I have had great success with 6922 & 7308 tubes.  All are interchangeable.

In addition, my absolute favorite is the PCC88 (7DJ8).  I have NEVER had a problem using these in ANY unit that uses the 6DJ8 family of tubes.

The National's are my favorite, (thanks Kevin!).

are 6DJ8 and 6922 tubes inter-changeable

yes in all cases

the question of preferences is very long to answer, and highly dependent on what gear the tube(s) are being used in and what sonic profile is sought - different circuits and applications have very different sensitivities to the specific make/type of 6dj8 used

in general, excellent 6dj8 variants are old stock usa or european made ones from rca/amperex/philips/mullard, though very good quiet ones, especially matched sets, are getting expensive

more cost effective options are old stocks from japan and eastern europe (hungarian tungsrams , yugo made ei's, czech made teslas)

6922 are  a similar tube ,the 6922 are a bit more rugged the classic Amperex especially white label D getters are one ofthe best verywell balanced, Mullards are warmer older Blackburn  type Also D getter , I am not positive on Siemens,  , Telefunkin German made Mazda made-in France ,

6DJ8 can be used in many of these applications and are very good value 

vintage tube services, or Brent Jesse Recording  are pretty popular tubes are getting pricey, 20 years ago 5x+less pricey.

@bdp24 Yes, they are equivalent can be substituted. If possible, try finding 7308 which is even better depending on sound quality your after. Some of the best NOS tubes include Amperex and Siemens brands. You can find a detail analysis about types of tubes and sound quality here:

https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html