My M-2000 sounds flat, boring and small. I haven't had a truly great tone from it in God knows how long. As a last resort I want to at least try swapping the 12AX7's in it (three of them.) I play lots of fat dub bass and push my tubes fairly hard with quite a bit of subsonic energy in the form of my various bass synths and filters. I have bought some GT's (12AX7R's) and was wondering what other tubes i should consider.....Mesa? I haven't tried the new tubes out yet. My GT's are Russian...what is the difference tone wise between them and a set of chinese tubes? I need a deeper tone overall; mine is just too "shallow." Folks seem to like Ruby? Thanks!