I'd like to share some experiments with you and see if you could add this feature to your firmware. I've tested some dsm modules (lp4dsm, hp6dsm) with a PIC and I've discovered that if these 6 channels transmiters can't transmit anything else than 6 channels, they can handle multiple receivers with different model number and different channel value for each. I've tested this with 4 receivers, each bind with different ID. I sent a frame every 5ms, so each receiver were still refreshed every 20ms.

So, can you add 1 or 2 more receivers in your firmware, and then be able to use 12 or even 18 channels?

For the binding, I suggest to use the 3 position switch to choose which receiver to bind.

This is interesting!

For the record, when binding, the TX module cannot do anything else. If it receive a standard frame, the binding ends. For a correct binding, frames for the other receivers must not be sent, and the period must stay at 20ms, no less.