This is a known issue with MOTU interfaces and the Apogee Big Ben, and the good news is, you don’t need to do anything. Here’s Apogee’s word on the topic:
“When a MOTU interface is connected without termination, Big Ben’s Termination LEDs light correctly when the MOTU interface is powered off, but indicate under-termination when the interface is powered on. When a MOTU input is terminated with a 75-ohm load, Big Ben’s red (over-terminated) LED lights. Thus, do not terminate MOTU inputs, as this does not affect clock performance.”
The Apogee website has an informative document on Big Ben and termination.