What were your settings?
I was worried about it being only 150 watts when I was contemplating buying mine. But really, you're playing stupid loud at the point it runs out of room. Luckily for me, we run all but the smallest of rooms with foh, and we're just a 3pc. In fact, I haven't even had the volume above 5, and that's without the shift engaged. The balanced out sounds better than really good..... It sounds incredible! The mids on the Shaw are a thing of beauty. I'm addicted to the 6th position.... It sounds and feels just like my b15.
Edit.... I don't notice any static or hiss.... In fact, I was surprised at how quiet it is.... But then again, the cabs I use with mine don't have horns.
Settings varied, but I kept the midrange in the 3rd or 4th position -- think I gravitated to 4th by the end of the night. Bass maybe around 7, though I tried it between 5 and 8. Treble I tried both pushed in (around 7, maybe a little higher) and with the "pull bright" engaged (maybe around 4, then). The Treble control strikes me as pretty widely voiced (and the voicing varies with the midrange selector switch position), with the "Bright" starting up higher, so you can get pretty different mid-upper mid-treble profiles between those controls.
Even with the super-deep lows the amp was putting out, it got louder with that cab than my former Markbass F500 did (the cab is 8 Ohms). The F500 barely tickled that woofer, though, whereas the Shaw was giving it a workout by the end. I think I started with the volume around 6, maybe a bit higher, but at the end of the night the volume was pushing 9. I said something about it after the gig. I did run the amp pretty close to "knobs at noon" for awhile.
"Stupid loud" varies with context, but we were louder than we needed to be. The amp was louder than I expected it to be but I think my GBE 1200 would go significantly louder, particularly while staying clean.
As for the buzz/hum, I bought the amp used so the tubes have some miles on them and FedEx gave it a bit of a rough ride (I did have it check out by an area tech)... Kevin Shaw suggested trying a new set. I've been told that tube amps are noisier than SS amps -- and the examples I've heard -- those I've noticed, anyway! -- would seem to bear that at least partially out. This is my first tube amp, though, so I'm not sure what to expect generally in terms of noise or of the effect that different/new tubes can have on the noise. No one remarked on it on the gig, but I was aware of it, a bit, between tunes. Sound man did not have a problem with the DI feed and he's told me before when he had.
Sounds like a fun gig, @MarkA! Thanks for posting your observations.

I don't run without the Fdeck in front of mine. I've never noticed any static either...
I might have to give that a shot. I'm reluctant to put anything in the signal path that I don't have to -- don't want to mess up the nice interaction my passive bass has with the front end of the amp -- but I might have to try that next time I want to play a loud gig with it. I don't think I'd use it for low volume stuff (though it could certainly be useful for taming a boomy room, in addition to conserving amp/cab headroom).