GAH! The fizziness in my PODXT tone is driving me crazy! I've tried using the EQ but as I'm a pretty inexperienced n00b nothing seems to work. One cool thing I've found though is turning the gain up and then turning the 'pad' switch on, as it not only turns the gain down but seems to make a decent bit of difference in the tone.
Anyway, if anybody fancies helping, I'm using the BigBottom amp model (surprise surprise) into the 4x12 Treadplate cab using an off axis 57, and a Screamer as the stomp.
The 'pad' is only supposed to decrease input level, so perhaps try turning gain down a bit more.
The usual recommendation is less gain and more mids, if you haven't tried that.
Not sure what to say about cab sims, but if you're running through a computer try impulses instead of the onboard cab sims.