Blu-ray Audio 2.0 LPCM vs. 5.1 DTS-HD


I have a conventional two speaker setup. Yet, on Naxos BD’s the 5.1DTS-HD option sounds much better, more detailed and open, than the 2.0LPCM.
I find with other record companies the sound of the options vary as to what sounds better.
I thought the 5.1 was designed for a multi-speaker surround setup.
Can anyone explain what’s going on?
128x128rvpiano
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I just have the two options of 5.1 and 2.0.
So I don’t know if it’s mixing or omitting.
It just sounds damn good in the 5.1.

In the future if I have a choice of mixing or omitting, which should I select?
I also prefer 5.1 DTS-HD from my Oppo 205 with balanced stereo analog to an Ayre KX-5 Twenty preamp.  The setting is down-mixed stereo.  For SACDs and CDs, I much prefer my Ayre C-5xeMP.

db 
If your hi fi system especially the speekers are good enough 2.0LPCM is much better. I found 5.1DTS-HD sound synthetic, artificial and over mixed.
I found the 5.1 sounded that way with my old player.
With the Oppo 105D it clearly sounds much more open and detailed and with better dynamic range.
It could be the source materials vary with each format.
My system is in the 15K to 20K range.