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?
rvpiano
Is that using a "downmix" option on the 5.1 or just using the two channels of the 5.1 and omitting the other 3.1?
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.