I am studying the mach 460 sound system for better replacement while keeping things as stock looking as possible. The 6x8 woofers are 8 ohm wired for 4 ohm load. JL audio makes an 8 ohm 6.5" subwoofer with little more than a 4" mounting depth. It will handle the same frequencies as stock up to the 300 hz low pass cutoff. Two of those should work fine in the rear deck as FlemWorld lists the box as having 8" of room. However the front doors are only 3 9/16's. If anyone knows off hand if thats from the sheet metal or the adapter I'd like to know because its close to another inch of room with the spacer and that's enough for it to fit. As for the midrange/tweeters, I haven't found any 2.5" speakers. 3.5's look like they will work but I haven't test fitted any, if someone has tried let me know. The rear deck could be modified for them but the tweeter pods in the doors pose the problem. The high pass filter is at 300 hz for the tweeters/midrange so aftermarket 1" tweeters will not work as they don't go below 2,500hz. That would create a hole in the frequency response. Most 3.5" speakers will work from 150hz and up, along with having a separate tweeter on the high end models it would round out the system and plug into factory wiring. To those that haven't examined a mach 460 6x8 woofer they are built more like a subwoofer. The surround is much larger then a comparable full range speaker. Aftermarket full range speakers will not handle the lows that the stock one's will. Does anyone know where to fit a speaker up front to take care of the 300hz-22khz frequencies?