The most active German forum for high quality car audio is
www.klangfuzzi.de. The user possibly most knowledgable about the Alpine PXA processors is old-diabolo. His homepage is
http://www.dreiradreise.de/ and it contains detailed infos about the PXA, inluding hardware mods. I hope you can make sense of it using Google language tools.
Having said that, I can't really imagine why people bother with these noisy things but to each their own.