I have both the K10s and Alto SXM12s and use both for monitors. The Altos are for vocals. You can hear yourself easier on them than the QSCs. I put some guitar in the bass players vocal wedge last week since he asked for it. And even put a bit of the slap standup in the guitar players one, although it was pretty heavily high passed.
I typically use the QSCs for sidefills or for keyboard players where intelligibility is less crucial that being full range.
I missed the boat selling the K10s off and replacing with DXR10s, now they aren't worth as much.
There's a venue I regularly play at that has a mix of K12s and K10s on stage. I really can't tell without looking which one is in front of me. Volume and intelligibility are roughly the same.
