Hi there.
Is it still in a car shaped enclosure? It would be interesting to hear this in a room environment. Very different designs.
Basically, the safe thing to do would be to purchase a separate amp for it. Then you can hook it up 'properly' to you receiver and have control the low frequencies it receives.
If you try to hook it to even just a single channel (say assigned as a front) on you Denon, it's going to receive the full frequency range instead of just the low frequencies that it would be limited to if it were attached to the proper sub output.
That means, whomever built your sub better have included a built in crossover component to block those higher frequencies, as the Polk driver by itself, just wasn't built for that and it will sound awful, at best.
So if your going to the trouble of building a sub enclosure with a crossover, might as well add the built in amp as well and do it right.
Note: This isn't meant to discourage you. Building and experimenting is fun.
