amb to sub?

The S12L74.  I already told you why.  The amp will run cleaner and cooler with a 4 ohm load, and that is the per-channel impedance used for just about all car audio speakers anyway.  And secondly, I'll reiterate what I said about power:  you will possibly never have this system loud enough to notice a difference between 750 watts and 1500 watts.

Then I went on to imply:  If you think you HAVE to run the amp at its max limit, and if you think you HAVE to power those subs to their max thermal limit...use the DVC 2 ohm models instead.  Usually this type of thinking is brought on by peer pressure from others who don't know as much about car audio electronics as you do.

Here is an SPL chart using a random sub I had in the WinISD database;  it doesn't matter what sub I use for this graphic.  The first link is a chart showing 118 db with 750 watts input:

750wattsspl.jpg

Now here is the increase in SPL when you double the power to 1500 watts:

1500wattsspl.jpg

You see about a 3 db increase.  3 decibels is the amount of SPL that is NOTICEABLY louder.  Now, of course, this doesn't account for the tremendous amount of cabin gain that will be added to the SPL level in a car, so the overall SPL will be higher.  But the point is that you may not be able to listen to levels that loud in your car whether it's 750 watts or 1500 watts.

Using those graphs as reference, if you were to imagine that the line representing, say, 116 db was as loud as you could possibly stand to play that sub, you see that there is absolutely no difference at all between 750 and 1500 watts because you never get it to that level.  Put a sheet of paper on the 116 db line on both graphs, covering the top part, and you'll see what I mean.

I hope by now my explanations are clear.  Good luck with your build.

very clear... thanks for your help.. i just wanted to be TOTALY sure that i wont be wasting money

again  thanks for your help...