I have a couple Alesis Alpha 112s - very similar to the Alto TS112s. I like it a lot thus far. I am fine with one. I agree - most PAs I've played on are in mono - or as Ross points out, best for the cool ping pong clean tones but lost on the gain tones.
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Guitars:
Strat PartsCasters (x2), 81 Ibanez Artist, 2012 Gibson Les Paul Studio, Epiphone ES-339 P-90 Pro
Effects:
Atomic AmpliFIRE, Avid 11R, Franklin ProDrive, Franklin F-Plex Delay, Line 6 M9