I have just installed a Phoenix Gold aftermarket speaker system in my xfire. The sound is unbelievable, and i am very stoked with this whole setup. Well worth the money...The components i used are:

Octane R 8.0:4 (4 Channel) amp
Octane ZR 6.5" splits speakers
Xenon 12" sub

I installed the amplifier behind the passenger seat. Unfortunately, because of the amp's size, i had to mount it over the cargo net compartment, but i don't use it anyway. Its actually kind of cool, cause the amp lights up in blue which leaves the passenger seat illuminated at night. The splits installation was perfect, besides having to trim the door panel slightly to fit the tweeters.

I installed the Xenon sub in a custom fiber sub enclosure. I have chosen a 'stealth' setup, where sub is completely hidden. The main reason was because i don't want someone to break into my car when i park at varsity. The sub dimensions are perfect...the correct volume to get quality sound (not thumping sound) and it matches the lines of the trunk. With the carpeted finish, the setup looks factory. I did have to sacrifice my trunk space, but there is still plenty left. All i have left to do now is to install a Alpine 9855 headunit and iPod interference and the system will be complete. More pics are in my gallery. Enjoy
tim.