Actually, to clarify a bit between BNC, AES, etc:
1. AES = SPDIF. Through a transformer. Via XLR. That is all. There is no magic to it.
2. Coax = BNC. With a different connector that offers impedance matching for GHz signals. This is very important for an oscilloscope. It is much, much, much, much (insert a bunch of "muchs" here) less important for digital audio speeds. In fact, it's likely that any "impedance mismatch" caused by RCA to BNC will be swamped by transformer ringing/trace routing/cable vagaries in any case.
3. If Eitr had AES, it would have to have an XLR connector. That's part of the AES spec. Which wouldn't fit in our standard small chassis. Which would have literally doubled the price. That seemed stupid, so we didn't do it.