Converting the x100 cable to USB

I currently have a CARK-91 and a bluetooth adapter I got from mobilefun/fonerange that plugs into the CARK-91 x100 socket.
I have been told by people I am calling that the sound quality is quite bad when I am using it for Handsfree via Bluetooth(BT) and figure that the BT adapter is just cheap rubbish.

I have a MDA Vario II (HTC Hermes) and it uses an enhanced mini-usb for its headset, charging is also done via the enhanced mini-usb.

So to improve on the Bluetooth connection I was thinking of taking my old CARK-91 cradle cable connector and wiring up my own Handsfree kit via a mini USB so that it charges the phone while on hardwired handsfree, thus getting charged phone and better sound quality (when it was hardwired to 6230 quality was fine)

Now questions
1. How feasible would this be? I havent been able to find the wiring diagram for the nokia cable yet, but in theory would it be possible?
2. When will there be or are there enhanced mini-usb connectors that can be purchased that can hook into the audio as well as charging? It seems that standard mini-usb will only do data and charging while with any carkit adapter I would ideally want both charging and audio.

The only enhanced mini-usb I have is on the standard issue headset which I want to keep safe until I get carkit sorted out :)

Any thoughts on above would be great.

thanks