Hafler effect setup - any concerns for a "ParasoundZonemaster2350" p-amp (or in general)

I have recently come across information on the web about the "Hafler effect" for creating a "studio" or "live venue" sound from a 2 channel system (such as most of us have). Basically it is implementing a third speaker located behind and centre of listening position with one speaker cable connected to + (red) of front left and one speaker cable connected to + (red) of front right going to the rear centre speaker + (red) and - (black). (** at least this is my interpretation/understanding of it **).

My question is, is this a dangerous set-up for my "Parasound Zonemaster2350" power amp? I have read that it can be catastrophic for bridged amp's and, my limited knowledge of bridged setups (which is none), I'm not sure if this would be safe to attempt. I have reached out to "Parasound" for their advice but pretty sure they will blanket statement recommend against so as not to take any responsibility, but who knows, maybe not.

Thanks in advance to all who reply,
much appreciated

That concept works for a non bridged amp configuration, it won't work for a bridged amplifier.   Do note that when you do that, you are taking L&R channels and subtracting them, when you take L&R channels and add them you get mono.  Subtraction gives you only the ambience information.   That is the good news, the bad news it also gives you all the noise, clicks, pops, and other nasties sometimes found on vinyl.   If you are going strictly digital, then this may not matter at all. 
This "Hafler" setup was sold earlier as the Dynaco Quadaptor, of Hafler design of course. Some Dynaco amps have this circuit built-in.


The amplifier must safely permit both front channels to be connected in this fashion or else you can damage the amp. Also, this lowers the equivalent impedance that the speakers presents to the amp. Some amps don't like low impedances. Verify that the amp will be safe with this circuit attached before going ahead.
Thanks for the info.

I did indeed go and check with my amp manufacturer tech department (Parasound) and there response was...

" I Don't believe this is possible with a Class D amp. Class D amps need a positive and negative run to each speaker. If you do try it, it should not damage the amp but might not give your desired result. "

So, upon that reassurance and others I went ahead and tried it. It works. It's not an amazing difference but it does give a larger 3D sound. What is coming out of the third speaker is low level ambience. The ambience opens up the size of the sound just ever so slightly.

Fun experiment. I'll listen for awhile to see if it will be permanent in my set-up.

I recall using the Quadaptor with Dynaco amps. It worked fine. After I upgraded to a more powerful amp that cautioned against going below 4 ohms load, I had to disconnect the Quadaptor. My speakers were 4 ohms and adding the Quadaptor with rear speakers would lower the impedance below 4 ohms. The sound was more enveloping while it lasted.
Just thinking outside the box here - you might consider a second amplifier in a Class AB design just to handle the ambience.  It doesn't have to be very powerful since you are subtracting the signals to get the ambience.   A fifth to a quarter of the power of the main amp should be plenty.
I’m just going to go at this as I’ve practiced it many times.

Normal front speaker set-up.  Take long single wire from Rt (+) to Rt rear (+).  Repeat same Lt side.  Connect both rear speaker (-) terminals with single wire.

If anyone sees this as wrong and wants to scream foul, then proceed.  As explained to me it provides out of phase material diagonally.  So Rt speaker out of phase material appears in Lt rear speaker, same with Lt speaker material.

I’m no engineer, have just set it up multiple times with success.  It broadens and deepens the soundstage.