OK OK Let me explain MY point of view here. < Last time >
I fix amps. I fix amps all day long. I fix more 4 channel amps then any other type or style < 98% of them run in bridged 2 and 3 channel mode >. I don't sell amps, nor do I install amps, except for my own. I fix amps for installers that screw up also < a regular occurrence over the 20 years or so >. I save installers ass's on a regular basis. So please don't hold it against me because I am here to do this for you guys.
WHY do I fix more 4 channel amps then any other type ? Please see my explanation as post earlier here.
I don't advise amp companies on how to sell their amps, nor have I been called in to show them how to build them either < maybe I should be though as I am not a salesman, I am a engineer> As I see a serious engineering short coming in the use of 4 channel amps in three channel mode.
Why is the MONO amps so heralded by engineers worldwide as the way to go ? Could it be the single power supply to a single channel design ? Could this be the correct way to control a amp and prevent its failure ? DUH !
NOW, why does this seem to be skewed across the entire 4 channel market of amps. WELL here again please see my post . Smaller 4 channel amps have more engineering headroom in the output devices then 200 watt per channel amps do because of the shear power that each output device is trying to deliver. The proper engineering term is S.O.A. < Safe Operating Area please see transistor pdf files the designers invented this not me. SOA is a listed credential of a output device.
SOA describes the MAX output current at a rated voltage, over a given time period without letting the smoke out of the device < and its way less than any of the other ratings for a transistor that you see on the page of info from the makers of the semi device.
I can build you a 50 to 100 watt per channel amp that will not blow out when run in three channel mode EASILY because I have a huge selection of output devices that will handle the excess power demands that the sub channels will see on a regular basis.
BUT when you get into the 200 watt range of output WELL the problem starts to become evident, And WHY IS THIS ? Well at these power levels The amp would have to have more outputs to handle the exponential amounts of power that will pass thru the amps output stage. And with more outputs comes a problem. If you run large arrays of output devices to get strength and durability to unbalanced loads them you must GAIN Match all of the output devices so they all carry a equal load.
Gain matching is time consuming and can be labor intensive to do it right. Now armed with this knowledge and the current low quality , low grade JUNK coming out of China. Do you actually think they care enough to gain match outputs into sets ? And what do they do with the fall out transistors that fail to be matched <sell them on e-bay I guess>
3 DB's is a exponential number not linear. Your hearing is exponential not linear. Exponential power demand blow outputs and fail amps.
If you want to run a Xenon in three channel mode I would add at least two more sets of outputs per channel just to handle the abuse the amp channels are going to see.
And why would I do this well why do certain amp companies do it on their 4 and 5 channel amps ??? Cause it gives you durability in a UNBALANCED load condition.
Now armed with REAL engineering knowledge and REAL repair statistics, YOU have been warned that their is a serious engineering issue when running a 4 channel amp in three channel mode.
IF YOUR CHEAP ASS CUSTOMER can afford a $800.00 4 channel amp they can afford a $200.00 bass amp that will last about as long as any other amp out their. And when they blow the bass amp up they won't be so confused by the loss of a single amp while their highs are still sounding so good.
4 Channel amps were built for 4 channel operation < make any sense here> because there are 4 corners or a car stereo install front to rear, unless your running 5.1 or 6.1 or 7.1 in a car.
If running a amp in three channel mode will get you the customer to spend your money I WILL TELL YOU ANYTHING I HAVE TO to sell you my amp. If it fails later on who cares.
Salesmen are salesmen everywhere, and I don't know of one salesman that has a engineering degree unless you sell semiconductors devices < its a requirement of the job to have a BSEE to sell the parts from the makers of transistors.
My business is predicated on service not sales, My business is to help people not screw them out of their money anyway possible, My business has a warranty. My business rides on my reputation. And my business requires engineering and science not BS and salesmen tactics. I deal in finite scientific based engineering level technology not laymen guessing at what happened here, I always see the results, and I know by the damage when a customer is lying his ass of about running 1/2 ohm loads.
Now you asked why this whole thing happened, I tried to provide a reasonable engineering based reasoning for your question. If you chose not to accept it, please don't.
I will continue to repair this engineering oversight, and paying my bills on a regular basis
< laughing all the way to the bank >
Nothing, the JL's on your bench for repair too!! 
