My first exposure to this unit came about when I was working at Hughes Aircraft in the early 1990's. At the time the company had been purchased by GM. They wanted to diversify and started an audio division. I was invited to a demo at work. Went into a room with a table that had two TINY speakers close together on it. An old Chuck Berry song was playing in mono. It sounded like crap, honestly. The demonstrator hit a button on the AK-100 and the room was FILLED with what now sounded like a stereo track played on much bigger speakers.
He put on a contemporary stereo track and started fiddling with the Center and Space knobs, widening the signal with Space and moved the vocals from the from of the mix to the back, where they could barely be heard. It was, (and still is), amazing. I was sold.

The Hughes SRS systems have come into favor by some recording engineers, most notably Tchad Blake, (who uses one extensively and has worked for the likes of Elvis Costello, Peter Gabriel, Pearl Jam, Richard Thompson, The Black Keys, Bonnie Raitt and U2...amongst others) and is used  to widen the stereo image of reverbs and delays, as well a stereo mixes. My understanding is if you use it on your FX, or on an electric guitar submix, it will sound amazing. The sound seems to come from well outside the speakers.

These units were discontinued nearly 30 years ago. My understanding is only 2500 were manufactured. They are very rare and sought after.

There's a great review from Audio magazine online, if you do a search.

Having several functions, it is mainly used for enhancing the stereo image to help create "3D" audio. If your speakers aren't positioned in an ideal location or you want more "Wow factor" from music or movies, then this is perfect. 

Unlike some other processors, this offers absolutely superlative sound quality in which you can have complete confidence. The patented SRS system uses the MID-SIDE method of encoding - adjusting - then decoding the signal. This is completely analog with NO SIDE EFFECTS. (No noise, distortion or anything like that. No cold, harsh digital processing) The Hughes AK-100/500 is a stereo component that deceives the human ear into hearing recorded sound in three dimensions instead of the normal two.The "sound-retrieval system" used in the AK-100/500 could improve state-of-the-art audio as much as two-speaker stereos improved upon hi-fi sets. It improves on a two speaker stereo system by creating the illusion that you just brought a band into the room. It creates greater realism.

The Hughes AK-100/500 component tricks the human ear into thinking that sound waves are beaming to the listener from different directions, much like natural sound or an expensive arrangement of a half-dozen speakers used in movie theaters. The component works with any two-speaker stereo system.

The system creates the illusion of listening to a live performance by "retrieving" the characteristics of natural sound, spatial cues that distinguish the directions that different sounds are coming from--which are picked up by recording microphones yet masked in the recording process and "buried" in the mix.

With this unit, the listener is not stuck in a particular sweet spot, and it maintains the sound quality when the listener moves or turns his head, turning a den into a concert hall.

I do not have the manual, but I will include my email address on the packing slip, so we can arrange for you to get PDF copies of the AK-500 owner's manual/handbook and user's guide. I will also add PDF reviews from Audio magazine and Popular Science.

The unit is in FULLY TESTED and in perfect working condition, lightly used, with some very minor scratching/scuffing/surface blemishes. (see pictures) S/N A099201254.