trying to figure out how to get a aux in connection for an mp3 player for my 97 e39 with dsp without spending $150+ on the cd changer adapter alone and came up with this scenario (which has other benefits)

1. upgrade my c33 tape head unit to the cd53 from an 03 X5/525 (which has an aux port on the back)
2. Install the Radio Auxillary Input kit (82 11 0 149 391/389 $40)

so i know that adds up to more than $150, but it also gives me an in-dash cd player and improves the overall sound of the system (according to a bmw product manager post I found elsewhere) before I start investing in speaker upgrades and whatnot...

anyone know of a reason this would not work? the person selling the head unit says it will work, but looking for a second opinion before I pull the trigger...

thanks,
remedy