My 990 was one of the first. Its 5-year warrenty was up June 20, 2010. For several months prior to June 1st the front-panel volume control's 'up volume' function had become unstable. Finally the up-volume function failed from the front panel control. The remote up-volume function still worked.
I contacted Scott and the 990 was sent back to Outlaw on June 1st. I received it back - the first time on June 17th or so. Jim the repair technician told me that the he'd replaced the volume control; but, that he couldn't ascertain the failure mode of the defective control after disassembly of it. He had also upgraded the firmware to version 3.24. Additionally he told me he'd re-soldered the power supply connections. I didn't unpack the 990 for a few days in order to impliment some cleanup and maintenance on my whole system.
When I attempted to reinstall the 990 it would turn on for a few seconds, then there was relay clicking sounds and the unit would turn off. Being a retired electronics technician Jim then asked me to pull the cover on the unit and inspect the power supply area. I took digital photos and forwarded them to him. Nothing appeared out-of-order, so back to Outlaw the 990 went.
Jim confirmed the failure mode, but he couldn't find the source of the problem. He told that he finally disassembled the unit completely and reassembled it and the fault went away. It sat on the bench for several weeks burning in and being checked for 'gremlins'. I received the unit back on August 5th; and, have just partially re-installed it in my system. It is playing through the 7.1 input as I write this.
Of note given Jim's questions: The unit has been supplied from a dual back-to-back isolation transformer setup, with about 15mF of AC capacitors between the transformers (i.e. serious filtering and isolation). It has been 'on' continuously for about 5 years - I am 'old school' in this regard (internal capacitor preservation mode).
In comment: As background for my comment - I have very large DIY panel main speakers that are tri-amped. The woofer section for each side is 12x6.5", the mid is a BG-75 planar-magnetic, and the tweeter is my custom made 6' long true ribbon.
At the same time as I purchased the 990 I bought an Audigy 4 "Pro" 6-input and 8-output soundcard for my computer. The tout for the D/A converters in this unit is that they were 'special.' Over the course of the past five years I have setup that computer as a media server system. I have attempted to use the 990 as a 7.1 'volume control' and bypass its internal processing by setting the main speakers to 'large.'
Within the context of long term observation it seems to me that the Audigy 4 Pro D/A converters might have superior sound than those in the 990 - using the 990 as a volume control.
My website has been moribund for 5 years or so, and is sponsored by another. "Acoustic Line Source Research" googled might get you there should you wish to see material on the large true ribbon or the BG-75. Apologies in advance if the internal links of the website are not working correctly, as I have no control over that matter nowadays.
I now need to begin the tedium of complete re-connection of the 990 to my complicated home theater/music system. Bob Marley sure sounds good - I have missed the 990, even just as a volume control. I look forward to exploring the 3.24 firmware changes.
I hope your 990s don't get gremlins like mine did. Oh, one more thing. The first time Jim sent the 990 back to me he had not put a "Warrenty Void if Removed" sticker on the cover/case junction. There is such a sticker there now - and I'm glad Jim confirmed the turn-on/turn-off failure mode when I last spoke with him.
I like Outlaw, but knowledge is power as they say. Hope this advises and helps.