Hi Gonk,
I am considering the purchase of a 7100 amp and was planning to bridge 2 channels to drive my passive subwoofer. The way I would do this is by connecting the sub audio line to one channel and invert this signal (I have a small line inverter box) to connect to the 2nd channel; the woofer would then be driven from the 2 red terminals, the plus from the non inverted signal and the minus from the inverted one. My woofer is 8 ohm, but in this configuration, the amps would see 4 ohm which should not be a problem for the 7100.
I would appreciate your feedback on this.