I wouldn't say they will play louder at 2 ohms as that only means the amps will achieve full power sooner on the volume dial due to the lower resistance. I would suspect the 2 speakers colocated similar to subs colocated would add 6db, yes/no?

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70