If Im not mistaken all of the radios use an amp of some kind in the back cubby hole on the drivers side. If its a nav radio there is a radio module under the spare tire but both the base model and the nav use the same amp in the cubby hole on the side. The dsp does the same thing but has a dsp amp in place of the normal amp.

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Just BMW's - All cars and trucks was two pages long
1994 318is
1997 528i
2000 323i
2001 X5 3.0 auto
2005 X5 3.0 auto
2011 535xi auto
2013 X5 xdrive35 Turbo
More are at my website

Aftermarket E53 Radio Install