Wiring encoders directly to GPI pins has been discussed many times in the forum, e.g. here. I never do this so don’t have direct experience but I have contributed to helping others do it so, please read through the linked post to see if you can get it working. Basically:
- Choose unused GPI pins (3 per encoder) to wire to the encoder’s switch, enc-a & enc-b pins and connect gnd to the other switch pole and the encoder centre pin
- Configure hardware in webconf with these pins, using wiringpi pin numbering.
To load an instance of fluidsynth:
- Add an instrument engine.
- In the “MIDI Instrument/Synth” view, change category to “MIDI Instrument/Sampler”.
- Select “Fluidsynth: SF2, F3”.
Depending on the hardware, changing group may be done by:
- Right / left arrow buttons.
- Rotate encoder 3.
- Swipe right / left on touchscreen / mouse.
- Drag up / down or right / left the “Category” display with touch / mouse.
If you are using a HID keyboard, either directly connected of via VNC then you can use the default keybinding (conigurable and viewable in webconf INTERACE->UI Key Binding) to do this. By default, left and right arrow keys are probably the simplest.