An update just in case anyone happens across this:
Turns out I had a 120 V amp. When my first unit was replaced the note about 240 V was missed or wasn't there in the first place, so I ended up with a 120 V. No surprise I kept popping fuses!
The Massdrop folks have been very communicative throughout my protracted troubleshooting effort. I'm returning the 120 V one I ended up with for a refund.