My friend, Sandy, is having good success adding a layer of ambience with a rear-positioned second set of speakers fed from an old Audio Research SDP1. You can read the late J. Gordon Holt’s evaluation of it here.
Essentially, the device extracts the difference between the left and right channels, adds a bit of delay to the results, and then offers that signal as separate outputs intended to feed a second stereo amplifier and loudspeaker pair.
The second pair of loudspeakers are placed behind the listener so as to provide a sense of realism one cannot achieve with stereo speakers alone.
The idea was originally developed for commercial purposes by the late David Hafler in what’s known as the Hafler Dynaquad system. If you’re interested in trying this for yourself without owning the processor, check out this link.
I have played around with this type of system and it really works. It’s more than a made up surround feeling that many SSPs provide. Those are gimmicks not worthy of your time. The Hafler system derives the ambience from the actual recording.
The thought of making a more modern version of this technology as a PS Audio product hasn’t escaped me, but alas, we have too many projects on the books as it is. I am quite certain the hint of suggesting a new product not already on the schedule would have me drawn and quartered.
And here you thought there was nothing left for you to do while stuck at home.