Can 2-channel be improved by using subtle surround Eno style?


Audio tweaks abound to improve sound. Components are swapped. Speakers are endlessly repositioned. How many have added a third speaker with a filter and volume control to subtly enhance spacial cues, Brian Eno/Hafler style?

These cues are easily accessed by connecting a stereo amp's +,+ terminals. (See caution below)

After all, these cues are the ONLY technical difference between mono and stereo. If you prefer stereo over mono, it follows you might prefer 3 channels over 2 channels. Like most things audio hearing is believing.

So, can a 2-channel system be substantially improved by amplifying independently a "Third Channel?" Multiple choice:
A) Stereo is 2-channel, 2 speakers full stop. Go back to the 70's or use a home theater system.
B) Once you hear GREAT 2-channel, you'll realize nothing and I mean nothing is missing.  
C) Yea, I get it, have heard it done well and it's not my cup of tea.
D) Yes! Everyone should adopt. All audio gear should support a Third Channel as standard equipment.
E) Other ____________ .
If E, Other...Respond to this thread IF YOU CURRENTLY use this rear/side/ceiling Third Channel or IF YOU PREVIOUSLY used and decided against.

The Hypothesis: world-class audio can utilize 3 distinct audio channels: Left, Right and reverberation or the so called, Third Channel. Specifically, the Third Channel is the signal difference between the stereo L and R audio channels. It's the ambience, echo, transients and spacial cues of stereo, non-existent in mono.

(Trying to stay away from discussing heavy handed, discrete, surround-processed techniques such as Dolby, Dts, etc. Key here is to subtlety improve a soundstage.)

The 4 potential sonic improvements of a Third Channel:
1) Enveloping 3-D, immersive soundstage. The z axis (depth) is enhanced. Some tracks are astounding. Details are enhanced. Often described as more liquid and enveloping soundstage.
2) HT or home theater are perfectly suited and are encoded for the Third channel. Obviously, the big advantage is no change of a stereo system is required when switching from HT to music.
3) Low level listening. Similar to Fletcher Munson curves, the +,+ signal is a lower level than the in-phase main speakers signals and perception of spacial cues and transients drops quickly at lower volumes. If amplified proportionately (increased), it blends well at low levels and is one of the few options to enhance spaciousness, as you decrease main L,R volume.
4) Live music sounds like the performance space. Concert hall, church or small club, these tracks flourish with an amplified Third Channel playing.

Advanced Set-Up.
It can be problematic using only one power amplifier as was advocated by Brian Eno or in the Hafler Circuit. (see below) A more sophisticated approach uses a filter to block low frequencies below 500hz, a preamp with two pre-outs with independent volume controls, a pair of mono-blocks for front channels and a dedicated stereo amplifier for the Third Channel.

Done well, 3 channel listening seems universally compatibility with all music and videos.

The "David Hafler surround" https://en.m.wikipedia.org/wiki/Hafler_circuitor Brian Eno third channel was popular before the multitude of discrete surround systems emerged. Bob Carver called it Sonic Holography. Paul McGowen, Spacial Audio Projector and Jim Fosgate has the SoundStage Expander...all patented products.  SQ Quadrophonic systems used 4:2:4 system that has come gone. But let's NOT make this thread about the history of multi-channel. Please see above Multiple Choice Responses: A,B,C,D or E (fill in the blank)

CAUTION: You've been warned! Try at your own risk. Use +,+ only with a non-bridged, negatively grounded amplifier. 
Ag insider logo xs@2xjimofmaine
Short and sweet: been there, done that, don't bother.
Yes.  The Hafler circuit was my introduction to surround back around 1970.  One can do so much better today with discrete multichannel.
I also like the Neo6 music mode quite a bit.  If you have a center channel already, I encourage you to try it.
If you have large floor standing speakers, adding another large speaker doesn’t improve the sound as well as just upgrading your main speakers. Budget wise, it’s a bust vs two better speakers.

EDIT: Same reason Quad was DOA. 
Short and sweet: been there, done that, don't bother.
Why not bother? If the +,+ contain the information unique to stereo shouldn't it be respected? Otherwise, go back to mono with 2 speakers, which can sound quite good. That's what you seem to advocate by dismissing. 
Third channel audio has been around for a long time as a possibility. Nowadays, proper cabling and tweaking can get at all those details and missing info, or at least I've been able to. 

Been in this hobby as an nothing more than an amateur for over 40 years and to this day, I extract more info and a more satisfying listening experience, and that's with just two channels. Don't give up on stereo just yet.

All the best,
Nonoise