I've run a 1x K120 cab with my Mesa Transatlantic for practice, practices w/drummer, and small gigs.
I've never really considered a minium output wattage to the JBL, but at 6 watts at bedroom volume, it's functioned flawlessly for hours.
If anyone has an idea of the low threshold, I'd love to hear it. I don't want to trash my JBL's, but even at talking volume...they sound awesome.
"Hi Ho...the Carrion Crow...FoldeRoldeRiddle"