Okay, here's what he said. His situation is different and doesn't help you much. He retained his HiFi amp so it is driving all of his speakers (aftermarket). He had to disconnect his component tweeter in the front from the crossovers and run them off BMW's stock tweeter input from the HiFi amp.

So, what I think is happening in your case is that the aftermarket head unit is trying to drive 8 pairs of speakers... which is not good, obviously. Unless they were 9ohm speakers for the fronts.

Can you take a picture of the OE amp harness in the left side compartment of the truck? And another of the radio harness plugged in under the spare tire. We need to figure out how all these speakers are wired.

__________________
2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)