Okay Colleen, the point's been made that the sub calibration isn't very complicated, but now the question of how to connect the sub has gotten a bit tangled-up in wires and cables. Since your 685 has no separate sub output but has both A and B sets of main output terminals, the simplest thing is to just keep the M60s connected as is(presumably to the A terminals)and to use regular speaker wire from the B terminals to the high level input terminals on the sub. Then, instead of selecting just the A output on the 685, you'd use the A+B parallel connection to drive the M60s and feed the sub a signal. Since a full-range signal would be coming into the sub, the sub's internal crossover would be set to roll off the response above a certain point(e.g.60-80Hz). Although there's sometimes a misunderstanding on the point, the sub's internal crossover doesn't affect the main speakers in any way; it just rolls off the sub on the top end.
As Jonathan and Rick mentioned, there's a way to use the pre-outs on the 685 with Y-connectors, cables, etc. to connect to the low-level input on the sub, but there's no good reason for that complication unless you'd also want to buy high-pass filters (about $25) for the main inputs to roll off the M60s below 70-80Hz.
