Welcome to the forums. I am sure you have said WOW like a hundred times already in the difference you are hearing. Congratulations on a great system. As the pictures describe you are kind of limited with placement options on your rears. Honestly the best thing to do would be to play some DVD's that are rear surround intensive and see if the rears are doing an acceptable job for you. You can always adjust their positioning (#$@%^&* drywall holes!!!!!!!!!!!) Fortunately due to the design of these particular speakers they will have a wide dispersment. You can play around with the subs placement and be amazed with the difference you will hear. There are really some great articles on this site for sub placement optimization, so check them out as well.
SO now for a couple of questions;
1. I see an accoustimass module so I am assuming you had a Bose system before, have you been actually blown away by the Bass you are now experiencing? I understand that those Bic subs are quite good.
2. How about the overall fullness of sound you are getting now as opposed to whatever you had before. I am sure night and day probably do not do the difference justice.
Anyway welcome and be sure to sit down relax and ENJOY the system, sometimes we get so caught up in adjusting and positioning and stopping the song in the middle to hear another sometimes you just need to relax and LISTEN!!!!!!!!!!!