I just purchased an REL sub The Q150E. One of the main reasons is the unique set up which provides a high level and low level input. The low level is the traditional rca input that is used for the LFE. The high level is a proprietary connector (sub-side). The other connection is down at your main speaker connections on your receiver or amp. They provide a level control for both the high and low level inputs. The idea is that for music the high level signal sends the same signal as your main speakers and the roll-off is controlled by the sub. It works great at filling out the bottom end on music and even SACD and DVD-Audio. The key is you must set up the main speakers for "large" so a full bandwidth signal is sent to the sub.
My experience is new with this brand, model and hook-up but my first impressions is that it is the most versatile sub I have seen for music and providing accurate control for music.
My experience is new with this brand, model and hook-up but my first impressions is that it is the most versatile sub I have seen for music and providing accurate control for music.