You could try:
-Using an MXR Microamp or similar boost pedal to hit the amp's preamp a bit for a bit of dirt.. big volume jump, though.
-Using a "transparent" low gain OD pedal; it'd work for your clean channel and not effect the gain channel a great deal
-Getting some hotter pickups, or just jack the current ones up a little bit for more output.
-Get some higher gain preamp tubes- a quick poke around most tube store website's descriptions will help you find the hotter ones.
-Get your amp modded for more preamp gain.
I wouldn't bother with those "volume boxes" off eBay, all they do is lower the amount of preamp volume going into the power stage by plonking a pot in the FX loop- proper attenuators go after the powerstage and before the speaker to properly dampen the poweramp's output.
If you're just using the clean channel and letting pedals do the work, you might wanna try dialing in a low gain setting on the Drive channel- should be a bit warmer than the clean channel and gives control of how much preamp distortion you'll have.
