I have a V50 2004 Momentum with High Performance audio system. I have a cd-player and radio and that is everything. I want to upgrade to get some more possibilities of playing music. I have heard it is easy to install an AUX-port and also a CD-changer.

This is good but are there other opportunities which are not that simple? I'm thinking of an Ipod docking station for example. Everyone says it's not possible, but is it really impossible or is it just expensive and difficult to get it to work?

It might be easy to install the upgrades, but if you have a either a fitted phone or Sat Nav, you might have a problem with the GPS BOX which is fitted in the rear right wing of the boot.
I have the same system as you, with an added phone and Sat Nav.
If you do get it sorted i would like to know all the info so i can do it also.