Both the mono as well as the stereo channels are perfectly quiet, as far as line-level gain staging goes–it was, in fact, the first thing I checked once I turned on the unit. I have not checked the mic-level inputs; the instrument inputs seemed perfectly fine (and these pass through the same mic preamp).
Regarding the build quality, the PCB-mounted potentiometers used by Presonus do not feature a threaded surround (as do the Mackie units, used to secure each pot to the front panel). That said–having taken my original 1202 VLZ apart many times, I can't say I'd miss 'em, especially on a $499 street price unit with the bells and whistles that the AR12 has–nor do they prevent shearing of a potentiometer shaft off the pot itself, which has happened a few times with the Mackie.