1) Backup your phone with iCloud.
2) Restore your phone to 5.0.1 using your computer.
3) DO NOT restore from any backups, set the phone up as new.
4) Sync your music over.
5) Try to play it in your Focii.
If that does work, continue with step 6. If not, see step 8.
6) We need to restore from your iCloud backup. So from your phone, navigate to Settings -> General -> Reset -> Reset All Settings. This will bring back the iOS 5 welcome screen where you can type in your AppleID and restore from your backup we made in step 1.
7) Try your phone again in your Focii when all your data is restored.
8) If you can't play music to your Focii with a factory restored phone, it would be best to find another Focii to test on. It doesn't matter if it is a friends or the dealers. If it still does not work, the USB interfacing with the iPhone may be defective and may require a replacement from the Apple Store.
Also on an unrelated note, just got the transmission TSB done...much, much improved shifting.
And on another unrelated note, I rode in a Audi A3 diesel today. Very, very similar to the focus. My very quick opinions:
The focus seemed more luxurious...nicer materials.
The Audi shifted MUCH faster and crisper.
That's about the only differences I could tell. Size, layout, storage space was all almost identical. It is very obvious that Ford baselined the new Focus on the A3.