Unbalanced connection should not be a problem, the A7s have RCA input connections.
Volume is about 14db lower in unbalanced connection but should be plently left in your avarage control room.
Why would you need a cross over ?
B2526w asw-650 image by maxxnmt on Photobucket
The sub already has one.
Or are you planning for a setup where you can control the sub's volume seperatly from mains?