is this amp good enough?

I'm about to install a system into my '06 Explorer. I have a Kenwood KAC-7521 800Watt peak amplifier http://www.crutchfield.com/S-dqzm0LKNPnU/App/Product/Item/Main.aspx?i=113KAC7251&search=kac-7251

Now I had 2 12" pioneer subwoofers that were in my old truck, but they are no good any more, and weren't loud enought (only 150 rms). 

I'm thinking about getting one of these  http://www.pioneerelectronics.com/PUSA/Products/CarAudioVideo/Subwoofers/Champion/TS-W307D2%7CD4

Its 1,200 watts Max , and 400 RMS. 

My question is which sub should I get the 2 ohm version or the 4 ohm version?  I think when the amp is bridiged it runs at 460 watt rms x 1 at 4 ohms.

I have no idea what 2 and 4 ohm means, Will it be louder with a 4 ohm sub? 

Thanks in advanced

I plan on adding just 1 subwoofer.  So 1 4ohm subwoofer should be good right?  As for the box, the sub calls for a 1.25cu ft enclouser with a 3"dia x 7.5" port.  Or a .86 cu ft sealed box.

Which would sound better and louder?

You will want to get the dule 2 ohm speaker if your only going to run 1 sub. Then you will want to hook it up in series and you will then get a reading of 4 ohms. when bridged on that amp. With that you will be able to take full advantage of your setup.

As far as the box really depends what your wanting to do. Also are you building the box yourself? A ported box is harder to build then a sealed box.

Here ya go I was not able to find post I also did not look too hard. But here ya go I used google.

Check this out it tell you how to do it.

http://www./help/Articles.cfm?id=68

I was looking on the site and found this diagram.  I figured that I would wire it up like the 2nd diagram for a 4ohm load, since my amp is 460 watt x 1 bridged at 4ohm

https://www.the12volt.com/caraudio/woofer_configurations.asp?Q=1&I=22

is this correct?

Thats correct! Like I was explained in my other post and it's the perfect load for the amp and it's not over working your amp. Then just read the sticky on how to set the gain and leave it.