What you could try:
Set all “Latch” switches to ON (so they keep playing until the trigger pad is switched to OFF).
Then put all the eight trigger pads into one radio-button group, so that only one can be switched ON at a time - in theory that should do what you want. If it doesn’t work, i maybe could have a closer look at it tomorrow.
…or you give this other concept a shot - could work even better for your purpose:
