Hello

From my experience with Yamaha keyboards I expect that for using the USB connection of the Abacus you need an Midi-USB driver installed on your PC which is specific designed to connect to the Keyboard OS drivers. For this you can consult your manual of contact WERSI support via www.wersi.de

I checked the WERSI WEBsite for download of such a driver but could not find anything more than the OAS updates.

If you want to use the Midi connections of the Abacus these are standard interface. So you need a pair of midi cables and
a USB-midi interface for your computer, like Edirol UM-2EX
There are quites some of these devices on the market, ask a computershop or music instruments shop. Or search the Internet for shops for USB-Midi.

Some of these devices are a combination of the midi cables (In and Out) and the USB connector. like the Edirol UM-1G (49 US$)

I suggest first to try to sort out the WERSI USB-MIDI driver
availability.

Cheers Jaap