I want to combine my M1A with a soundboard transducer (SBT) pickup. I would prefer to use my M1A since A) I already own it and B) I like having the volume control. Can I use the M1A or would I be better off using an M1?

Do I need to get something like a Switchjack to combine the two pickups? It looks like the ring is already taken on my M1A jack.