hmmm, aggressive tone & more lowend - sounds like you want some 6550s in the output stage.
As for ECC83s (aka 12AX7s), I only ever use NOS preamp valves as I have a huge stash of them and the tone is much better than anything currently being made. If I had to choose though, for a gainy amp I'd say most Chinese ECC83s tend to have alot of gain and cope well with high gain. Dont spend a fortune of the 'super-duper gain-tested' ones Watford Valves sell, just the normal ones will be fine.
:twisted: