"Bypass" mode will only send a full-range signal to your mains if they are set to "large." If they are set to "small," there is still some type of filtering applied. As far as I can tell, it's a firmware bug, and is being worked.

Check this thread:

http://ubb.outlawaudio.com/ubb/ultimatebb.php?/ubb/get_topic/f/34/t/001287.html