I installed a couple weeks ago - - 05 E53 4.4 DSP non Nav - - Very easy install, took around 20-25min once I did my research around the web...time included finding tools, appropriate drill bits...
Pulled the vol knob off the radio, used appropriate hex wrench to unlatch, hinge, and remove radio out of the way; found the empty plug in the back.. plugged cable in. Removed climate control (easy, just push it out) for more room to maneuver.
Ran the cable to the ashtray where I drilled a small hole above the CIGARETTE EXTINGUISHER, and a larger hole in the back of the ashtray to feed the cable through...mounted the aux jack in the small hole, and that was it!! $45 on amazon well spent. Select 'AUX' with mode button and begin listening to your iPhone/Pod in your X.
Enjoy