The 7308s will work fine electrically. The most likely overt change will be improved frequency extension, punchier bass possibly but I doubt thunderous bass, typically better clarity, definition, air and greater transparency on the top. It all depends on the tube you buy. Be forewarned there are alot of rebranded, counterfeit and junky 1980s vintage ECG type 7308s not to mention poor quality used pulls sold as test new.
If you are happy with the Bugle Boy 6922s it might be a good idea to stick with them.
If you are happy with the Bugle Boy 6922s it might be a good idea to stick with them.