Posted on behalf of another E2E user...
It looks like the DS125BR401 has RXDET which allows the user to manually select a 50 Ohm termination on the input, high-impedance, or automatic input termination selection based on receiver detection. The DS100KR800 doesn’t have this. Is the DS100KR800 always in 50 Ohm termination mode or is there a separate way to enable it?