Need help installing aftermarket stereo

[Fr0st99]

So I've talked with a few people and tried going to a few car audio places to see if it is possible to install an aftermarket head unit in my 2003 X5 3.0 with DSP. Some say yes with a lot of work while others say it's not possible without getting a new amp and rewiring everything.

All I am trying to do is install a Pioneer DEH-P7900BT without having to upgrade the rest of the audio equipment in the car. Does anyone have any experience with this and if so what is my best plan of action???

Just to throw it in there - I do have the Pioneer Avic F900bt that I would love to get in there...