I use a Niles MSU140 repeater with my system (including a 990) with no problems. I have the sensor mounted in the ceiling near the screen so I can point the remote more up than forwards, the better to see the buttons, but near enough to the screen that anyone who points the remote at the screen will catch the sensor.

I use two Niles IRB1 blaster type flashers in the closet, mounted facing the 6' high rack front at 1/3 from the top and bottom. One flasher alone didn't reliably catch all the equipment sensors, but two does the trick.