To clear up:

The way I was tinking about requiere a external switch, is there a way to switch with the "source" button on the headunit like the orginal device do?

Hi, and thanx for your expertise in Pioneer's IP-Bus and electronic!

I have a MD-P100 (IP-bus in and out) and a old CD-charger (IP-bus out). I was told if I was planing to use both of them I needed a device costing 100$.

Hmmm...  can't I make one for myself I thought. And here I am

The easyest way must be to switch the 5 cords in the IP-bus that acually transmitting data using relays or something electronic.

Any other ideas?