wiring 2 12 4 ohm l7s to bxi1606d

The top picture is what you want to do.

there's no bridging involved, bridging happens at the amp, and a single channel amp can't be bridged.  You're just wiring coils in parallel and subs in parallel resulting in a 1 ohm load at the amp.

you could also run a seperate speaker lead for each sub as long as both subs' coils are wired parallel the amp still sees 1 ohm.

there are two pairs of speaker outputs to allow for easier connection of multiple speaker leads, not beause there 2 channels out of the amp.