I didn't want to wait for my triwing to arrive so I took a flathead and managed to get the screws out. Since I also don't have my rotary tool at the moment I removed parts of the battery compartment with a knife, pliers and my soldering iron. The parts I didn't remove are the two screw holes, the part that holds the audio jack and the part responsible for holding the battery door in place.
This doesn't need to be pretty, it'll do its job behind a closed battery door anyway. While I was in there I also cleaned the button pads and what else needed cleaning in my opinion.
Because I'll be wiring the headphone jack to the output of the USB sound card instead of prosounding it, I won't be needing most of the daughter board, so I cut off the part that that the jack wasn't soldered to so the electronics won't bite my ass later… better safe than sorry. I also cut the four wires on the main pcb, because they weren't attached to anything anymore. I also removed the speaker.
Finally I measured where the pins of the nanoloop USB MIDI adapter go when it's plugged into the link cable. the switch-up between pins 2 and 3 is correct, they're a twisted pair. what's IN on one side is OUT on the other.
Before I'll continue any further I will wait for the USB hub to arrive because it determines how I'll arrange things in the newly won space. Hope it won't be too long.
I've decided to solder the 5V and GND of the incoming USB cable (the one belonging to the hub) to the two battery terminals that are left over when the time has come. I hope I'm correct in assuming that this would work just as well as soldering them to the power connector.
everybody here is invited to learn from what I do and improve upon it, I'm just pioneering the work. In fact I would be stoked if anybody who knows more about the DMG and electronics than me will step in and streamline and optimize the process.