stereo help adding a sub

Right now my boat a mobius xlv just has six polk db675 running of the head unit. I want to add a sub to the drivers foot rest. There is plenty of room to do a sealed or ported box. I have been thinking about the image dynamic idq subs, from searching it seems like a good sub for the price. My question is should I get the 2 ohm dvc or the 4 ohm dvc sub. Also I want to power the inboat speakers and they are rated at 60 wats rms at 4 ohms. Should I get one amp to do it all or is it better to run one amp for the sub and one for the polks.

As far a which impedance sub you choose will have some bearing on which amp you choose. The 2ohm DVC can be wired at either 1ohm or 4ohm, and the 4ohm DVC can be wired at either 2ohm or 8ohm, so you need to find an amp with the proper Watts RMS output, at X ohms, that will best match the sub's recommended power handling.

Not sure which IDQ sub you are looking at, but Kicker makes a great 5 chnl amp that will deliver 210 watts @ 4 ohm or 420 watts @ 2 ohm and includes remote bass control knob. It will also power your 6 cabin speakers....Kicker KM700.5 (non-marine model = ZX700.5.

Have you by chance looked at the Kicker CompVR-10 sub? Will handle 400+ watts and can be used in an enclosure or infinite-baffle (free air).

Thanks I'll check them out. I was looking at the idq12v2.d2 or d4, 350 watts rms. Looking for something that will sound good without costing alot.

You've got 6 speakers powered by the head unit?

I'd recommend a good 4-channel amp to power those. 2-channels to power the 2 bow speakers, and 2-channels to power the remaining 4 in the rear of the boat. A 6-channel would also power tower speakers if you add them.