Yep. Plug that into the unfiltered line in plug on the back of the Polk. To configure it, don't worry about setting the crossover on the sub itself; you just bypassed that.
Run Audyssey on the Denon 1612 and let it pick the crossover setting. Should set the crossovers with the speakers to 120 or 150hz.
One thing. After you run Audyssey, see where it set the channel level for the sub. You want it to be close to 0db. If a lot lower than that, turn the gain (volume) down on the back of the sub and rerun it again. Getting it close to 0db optimizes the receiver output for the sub amp. Then if you want it bassier after running Audyssey, turn up the channel level on the receiver (not the gain on the back of the sub).
If this is your first time using a Denon and Audyssey, check out AVS member batpig's resources
. They are really helpful.