amp selection question

Here's how you should set up wiring on the subs:

Now, the "load" this will put onto an amp is 4 ohms.  An amplifier will make power according to the resistive load it encounters.  You'll see amp ratings with __watts at 4 ohms, etc.  This resistive load is what that is referring to.  So you have two subs each with a capacity to handle 250 watts of power....total is 500 watts.  Look for an amp that will output about 500 watts into 4 ohms.

You have the decision to look at either regular 2-channel amps or 1-channel mono amps.  With your subs, you would probably do better to go with a two-channel and use the bridging feature of the amp.  Look for an amp with the rating of about 500 watts X 1 at 4 ohms bridged.  The amp will primarily be rated for two channels at about 125 watts X 2 at 4 ohms.

I would suggest not going the 1 ohm load route at this stage of the game.  Get the two channel amp for a more versatile piece of equipment in the long run and a better overall install.  You can use less than 500 watts but you shouldn't try to use more and limit the power...... here is an example of an amp that would work and here is another.

Here is a good amp for a good price http://www.cardomain.com/item/MTX502. MTX's thunder 502, it does 500 watts bridged at 4 ohms so it'd be a perfect match to those Image Dynamics subs.