OK, here are the steps, for f900bt and x910bt users only:
1) Update the CE5 winCE firmware image using the following steps. For NA units, use the download on the fx3.1 page: http://avic411.com/index.php?/topic/27807-fx31-complete-firmware-image/, or you can use this one: http://avic411.com/index.php?/topic/22844-complete-30-install-guide/. For Euro users I have no idea which one to use. If you already have CE5 then maybe all you need is CE6. You could use the one from the Italian thread: http://www.mediafire.com/?48ga7b53x11xbqk. Here is how as per the fx3.1 thread:
1. Insert SD card into AVIC and turn it on.
2. When the pioneer logo comes up, press and hold the menu, map, eject and the reset buttons at the same time. When your screen goes completely blank, let go of the reset button but continue to hold menu, map, and eject buttons. This will bring you to a blue screen, telling you to reset the unit (ignore this), you will have to enter the service combination. Press the volume knob in this sequence and you will see * signs for each push: Up, Up, Down, Menu, Left, Right.
3. Select Wince Upgrade
4. Select Update SD Format
5. Wait until it says restart in the bottom center. Reset the unit and leave the SD card in.
2) After updating to CE5, flash the CE6 winCE image using the same steps as above. It is here: http://depositfiles.com/files/0gkvldr2i
3) Copy AvICnet on to your unit. Copy maps, pois, dem files, ect.
4) Reboot. That's it!
One thing to note, the CE6 is not actually an update to Windows CE6. It is just CE5 with a few updates and modifications (such as disabling the gyro).