Funny this question should be asked right now. I play the same amp, (4X10), and I also wanted it to break up earlier and get some better tube saturation. I was looking at the THD Yellow Jackets which allow you to use EL84's in place of 6L6's. The EL84's are lower power rated tubes and will probably only give you use of 30-35 watts out of the amps rated 60. What this does is now you have to drive your amp more to get the same volume, but with driving it harder you will get tube overdrive much earlier at less volume. These tubes also make the overdrive channel alot smoother than the 6L6 tube configuration.

THD and Groove Tube make these adapters. Tubes are included with the adapter. I have the Groove Tube version, set me back $120. Well worth it though.