After I took out my Mach 460, including the factory rear deck, I just decided to cut a 1/2" piece of MDF and bolt it into the factory bolt locations where the factory deck went. My Infinity speakers back there fit into place nicely using the new deck and I then contacted Infinity tech support and he said it would be beneficial for me to build two small boxes for each rear speaker. He said .25 cu.ft. of volume would suffice, so I built boxes to that and mounted them under the new rear speakers on the new rear deck. Haven't re-hooked the speakers up to see what it sounds like but it should work fine according to Infinity and hopefully it'll improve the lack of bass Infinity 5.25" speakers have. I don't think their is a lot of volume in the factory plastic deck, so building my own little boxes should work out well w/ my new, home-made rear deck. Good luck.