Thanks gonk. I recommend that, if the manual is ever revised, the IR section be updated. Page 9 of the 990's manual has an identical description to what's in the 970's manual:
"IR output (see page 22) Use this output to feed an infrared flasher attached to another piece of audio/video gear. Any infrared remote signal received by the Model 990’s front-panel sensor or by an external sensor connected to the Model 990 will be relayed through this jack, so concealed audio/video devices can be controlled by remote."

Someone who has owned both preamps would likely be expecting identical behavior based on the manual.

I guess I should thank Elmosaurus for being so detailed oriented and helping (at least me) understand our gear better. I would have never thought to ask.