I just installed an auxiliary port in my 05 fx45.
I tried to mimic the how to on the M forums but the 05 tape deck doesn't have the 3 wire plug they refer to.
So I found on the back of the board for the tape deck there is three solder spots that terminate on a tab off the board.
The spots are labeled Lft Chn" Rt Chn" & "Grnd" so I bought an eight foot headphone extension cord and cut off the male end, spliced the wires and soldered them right to the board.
For now I have the wire routed through the cup holder, but I am going to install an aux outlet in the center console soon.
The only issue I am having with it is I can only use it with a gutted cassette tape in the deck to "fool" the radio into thinking it is playing a tape.
The sound quality is good but when you turn the volume all the way to zero you can hear the tape deck running. lol. I will update you as soon as I figure out how to make it not need a gutted cassette.
Btw the gutted cassette is needed instead of a blank one because it will run to the end and stop the music and flip the tape lol