Okay, I think I see what you're saying. But I still don't think it applies unless I misinterpreted his typo.

I'm saying, the only way your description would be an issue is if a stray pin (any pin other than TX RX and GND) on the null modem cable made a connection from his external device to the empeg, or loopbacked to his device. But that can't be, because he said that at his device's end (assuming I read his typo correctly), it only has TX RX and GND connected.

And we know the empeg's sled connector only has TX RX and GND connected.

So even if the null modem cable put loopbacks on every single pin (other than TX RX and GND), it wouldn't affect either device. In this configuration, they're just wires dangling in midair not touching anything other than themselves.

The only way this would be an issue is if somehow the empeg sled was so badly miswired that another wire was connecting TX or RX to something they shouldn't be. I've never heard of that happening on an empeg sled. Or the loopback cable is so badly miswired that it's connecting other stray pins to the TX and RX.

Other possibilities are: his device really does use those other pins, I've misinterpreted his typo, or things are just completely miswired at his device's end.