6-23-17: I am using two new D700 subs and an older M&K dual 8" MK series sub in a AV system. This system is mostly for AV Surround. One of the D700s and the M&K are connected via LFE line level on a 7.2 configuration. The other D700 is running in the main stereo channels with B&W 685s bookshelf speakers. The main five channels of the system are driven by a Rotel 5x200 watt amp. The head piece is a Denon 7.2 surround receiver. For the main stereo channel D700 I have two connection options: 1) "Y" the pre-out of the receiver or 2) go speaker level into the D700. Certain sub makers extol the virtue of driving their subs with speaker-level inputs versus line level (some promote using both LFE line level and stereo speaker level (REL). Using speaker B from the Denon to the stereo channel D700 sub would allow me the option of switching that sub on and off via the B speaker switch - nice for set-up and flexibility in listening. Which connection do you think best for sonics on the stereo D700? Thanks in advance for feedback.