You should be able to understand the connection process from the BFD Manual. On the rear of the BFD, above each Input/Output you will see an "Operating Level" button. Make sure this button is pushed in (the "IN" position) which is for the -10dBV (HOME) setting. Do not use the +4dBu (STUDIO) setting (leave this button in the out position). Once you have your BFD connected then you are ready to set the input level. .....On the top right front of the unit you will see the "IN/OUT" button. Press and hold this button for a moment until the button light blinks. You are now in the "BYPASS" mode with no filtering active. .....The input level is monitored by the LED's in the far left section of the display window. If the unit is not in the "BYPASS" mode then the LED's will monitor the "output" level.
You're right, that's exactly what it looks like. I'll have to check when I get home what I've done to mess that up.Are your sure the sub was still getting a signal after you inserted the BFD? That "after" trace looks awfully like a plot of a main speaker only. Best check your cables and the connections you used on the unit.