Check this video at 8:05, see if that helps. My guess is that the RX1 pad is and un-inverted UART input, and the SBUS pad goes through an inverter first before it hits the UART. I did not watch the whole thing to see which port he configured as Serial RX, but I would guess it would be easy enough to test and find, but my guess here is port 1.
[MEDIA=youtube]iiD0xBbSyyk[/MEDIA]
