I have a Phase Linear 400 sitting in my closet, but when it was used for the rear channel it worked well with the 950. I am sure it would run fine on a 990. With 5.1 system you need to calibrate the pre/pro to your amps/speakers to get the proper sound output. If you want the loudest sound from the system, and you have all full range speakers, then 5 channel stereo is your ticket. Also, 110 dB is ear plug time for me. I rarely play my system that loud, and you may find that the room will fight you as the sound starts to cancel itself out. I know in my room, with levels that high, it is actually louder outside the room then in it.