There’s a problem that has been ignored by the entire music industry which I believe is really important to music-lovers that I think you might want to investigate. Approximately 32 years ago when digital media was introduced to the music consuming public as a media with “Perfect Sound Forever” the music industry made a huge screw up when it got the playback polarity of digital music on CDs and later DVD, etc reversed (inverted polarity). On a random basis that means that digital media and files are heard in the wrong polarity approximately 85% of the time and either 92% wrong or correct once their audio and video systems are set to a fixed playback polarity.

The bottom line is that the music played in inverted polarity sounds harsh and two dimensional which is probable the major reason that some music-lovers still believe (without knowing the real reason) that analog music media (that plays in the correct polarity over 99.9999 +% of the time and would also sound bad if played in inverted polarity) sounds better than digital media, when in fact it doesn’t sound as good. That often causes music-lovers to spend untold sums of money and time trying to smooth out the edgy and somewhat irritating and flat sound of digital media. This should be an object lesson on how an entire industry with its experts and electrical engineers can get it wrong and not do anything about if for over 32 years and counting!

But there’s some good news here because in many cases, all one has to do is reverse the connections of all their speakers wires at one end only to correct the mistake that’s free for the doing. For more on how do that, see the homepage of my website: http://www.AudioGeorge.com and scroll down to just below the credit cards I accept. Many in the music industry agree with me. I’m know in the industry as The Perfect Polarity Pundit Chief Polarity Buster of the Polarity Police and come companies send me their digital media/components to check its polarity, and do that pro bono for the sake of the music. I’ve written two monographs that go into great detail about the problem at: http://www.ThePolarityList.com, http://www.AbsolutePolarity.com, and http://www.PolarityGeorge.com

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While I appreciate the attempt to get things right, I'm afraid that like most people, I'm completely insensitive to recording polarity.
I have my fingers crossed the XLO Test CD Out of Phase track is in the correct polarity. 
I can easily switch the polarity of my system. Past quick experiments led me to believe I really couldn't hear any difference in doing that, on headphones or speakers. But now that you've brought it up I'll experiment some more.
"The bottom line is that the music played in inverted polarity sounds harsh and two dimensional . . ."

The OP is selling vaporware. Beware.

One of my DAC’s has a polarity switch. Yes, there’s a difference - and it’s minimal. In one phase, there’s slightly leaner sound that improves sound stage width & depth. In the other phase, there’s a slightly fuller sound that improves body. Nothing even close to harsh & 2D.

Take into account all of the equipment for the recording. Was each and every component and microphone in the same phase - including the sampled tracks from another recording? When the mixed tracks went to a different mastering house, were those components on the same phase? Highly unlikely.

I have my fingers crossed the XLO Test CD Out of Phase track is in the correct polarity.
My fingers are straight now.... Test successfully pass.... Only this test makes the XLO test cd valuable indeed....
Ironically perhaps Roger Skoff (please don’t scoff) - one of the XLO principals behind the XLO TEST CD - is not a big fan of a lot of the audiophile tweaks that have become semi popular over the years. Oh, well, you can’t please everybody. Dr. Keith Johnson is the voice you hear on the out-of-phase track. 
Engineers dont like simple tweaks created by ignorant fool like me for sure... :)

I dont give any money....
It has not been ignored. There was a big fuss 10 or 20 years ago, and all the DACs, CD players, and preamps had "polarity" buttons. Since many people can't hear the difference, and if they can don't have a strong preference, those buttons are become less common.
I flipped the polarity on my system and listened to a few CDs. I think ishkabibil may have planted a seed in my head. I can't say for sure that I'm actually hearing anything different, but I like the idea that it might sound better, which is making me believe it does sound better. Makes me feel all warm and fuzzy inside knowing the polarity is inverted. So for now I'll leave it that way. Other users of my system have made no comment on the sound quality since I secretly made this change.