I am going to run mine without the factory amp as I am stripping the rear end. I need that space for 'other things.' When I finally choose an amp my plan is to install it where all of the current factory radio items are in front of the spare. Plenty of room for cooling and wiring is just as easy. Unless I am missing anything else.

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E53 X5 4.8is-Dinan S2-Street Brawler
E70 X5M-The stoplight shocker
AMG E55K-539 RWHP, 629RWTQ-my toy
GX470-the unbreakable truck.
F30 328i-JB4 STG 2. Daily MPG Work Beater
02-WS6, 6sp my other toy
...other stuff parked around here somewhere