Hello Carlo
The second set of Midi channels are accessed through system exclusive data, (Look at the Midi port setting in the back of the SD 2 instruction manual) however you can normally access them using the LSB setting in Edit Midi Voices. (You will need to experiment here) Do not confuse this with the MSB command. (This is just for the voice banks)
If you just want the SD 2 for the styles and manuals, then you do not need more then 15 channels, just assign Midi 1 Out manuals to channels 1 – 7 (Wersichord has its own channel) and the Styles to channels 9 – 16. (Use the Sound setting not the Standard setting on Midi Manual 1 Out)
It is then just a simple case of using Quickload, Sounds and choosing the External 1 sound group. (You can also map the voices if you require)
Please be aware that the SD2 has considerably less polyphony then the Abacus, so this will limit the number of sounds it will be able to play simultaneously.
Hope this helps

Bill