What's nice about CSP2 and Taboo (only commenting on these as they're the only Decwares I've heard) - they don't need expensive tubes to sound really exceptional. It's something to note: they change the rules quite a lot and open the field right up - probably because they are (I understand) very simple circuits with excellent execution. I think this makes them highly transparent to tube changes and less fussy at the same time.
Whereas the Lyr demanded expensive tubes. I was gratified by the improvement I got from Matsu 6922s over stock and some other tubes, but never was I going to buy a pair of tubes that cost more than the amp itself!!
V-Duh, get Steve Deckert's advice about the 7DJ8. It runs at a different heater voltage. Steve does tricks with voltages himself, but this...might work, might not.