Presto Stark

Anyone -
I picked up a white 1997 limited edition anniversary 100 watt recently. It came equipped with EL34's, and runs through the matching 4x12 25 watt greenback cab. The other Marshall heads I have (or have previously owned) ran 6550 power tubes and sounded better to my ears. (Or what's left of them!) I haven't seen much discussion on the EL34 tone vs. 6550 or KT88 power sections, but I'm not that thrilled with the EL34 sound. Seems to break up way earlier, and thinner sounding than the 6550 equipped heads. Will changing the cap next to the pot on the bright channel fatten things up, or should I just re-tube and re-bias with 6550's? Maybe a 12AY7 in the first pre-amp position? Thoughts? And, that's a non-master volume model, based on Plexi circuitry...Thanks