Audio Systems: Subs cutting out, watts rms, power akoustic

Question
Hey, I have two 10 inch Phoenix Gold RSDC102 Subs hooked up to a RYVAL V8001 Amplifier.  My Subs are hooked up like this.
http://www.crutchfield.com/learningcenter/car/subwoofers_wiring.html?imageID=2DV...
I also have a Power Akoustic 1.5 Farad hooked up.  My problem is that after I Turn my stereo up past a certain volume level my subs cut out.  They will miss most of the bass notes but occasionally hit a couple.  It works fine at volume level 21, and most of the time at 22 (unless the song has lots of bass)  but if I turn it up to 23 it starts cutting out.
Could you please help me figure this out.

Thanks

Answer
Do you have the right gauge power wire?

It should be at least 4 AWG.

How do you have the gain or level control set?

Here is a guide that will help with correct gain settings:

http://www.datafilehost.com/download.php?file=6d26c621

You'll need Microsoft Excel, a multi-meter (AC volt-meter) and a way to burn an audio CD from an MP3. A 0dB 60Hz test tone Mp3 is included. You'll want to set it so each sub gets 400 watts RMS.

If you don't have Excel, use this link http://www.box.net/shared/nkkw1dhk4g