Hi
The RTi series is quite nice and A5s can deliver good lows at 30hz......if you have a little more budget the A7s claim to deliver as low as 20hz which then eliminates the need to add a subwoofer.
Between the 660 and 550, specs are same except for driver size (12 inch and 10 inch), I would go for the 550.
Profx ropes in discount between 10% - 15%.....make sure you demand for it.....
Audition and decide.....if you don't want towers, the 550s along with RTi A1s or A3s blend very well.....