I have a 2006 M35s with the bose speaker system and i am trying to keep the original head unit. Ive been researching the aux feature for the car and from what i can tell there is no way to use the “bose surround sound” feature. using cds works but for aux the option is greyed out. Is there any way to override this or will i lose the feature if i choose to use aux with my phone?

You will lose it. Aux is only 2 channel analog audio input to the head unit and to be honest it sounds quite bad even with the best of equipment.

Not sure if this helps but I installed a USA SPEC bluetooth interface. Allows me to play music from my phone on apps like Spotify thru the cars speakers. Works great, easy install. 5 min video on YouTube for our car.