DVDs with both AC3 / DTS

[TooNice]

I've come across DVDs with both AC3 and DTS for the same audio track (same amount of channels, that is 5.1, and same content). Assuming that I exclusively, use a computer for playback, is there any instances where I want to keep the AC3 track? Storage is not a major issue, so I don't mind using 3x more storage for the DTS track over the AC3 track if it is better. I also wouldn't mind keeping both tracks if there is any scenario where the AC3 is preferable.

I should note that I MPC-HC is my main player, and I usually use (high quality) headphones as I no longer have the space for surround speakers.

And while I am at it, I also have DVDs with both 5.1 and 2.0 tracks. Is it preferably to use the 2.0 track over the 5.1 track on stereo speakers / headphones, or can the software player do a good job downmixing 5.1 to stereo?

[Emulgator]

You may want to keep all audio tracks.
Downmix behaviour may well be different, given that the DTS stream can have its own downmix coefficients implemented.
I have a few concert DVDs where the AC3/DTS downmixes behave differently.
And the day may come where you will want to have your surround speaker set back.
(I came from 2.0, but I am at 7.0 now, no extra LFE, but routed into Main L/R)
For a 2.0 speaker setup the 2.0 stream was more useful in my cases.
But it all depends on the way the mixes are made up.
It is always interesting how these behave.

[mp3dom]

5.1 Downmix never sounds like the original 2.0. It's a 'compatible' way to playback a 5.1ch onto a 2.0 speaker set (tv in general), so you should keep the 2.0 if you want the true 2.0 mix.
DVD with only dts is out of specs, hence you have both dts and Dolby Digital inside the dvd.

[TooNice]

Thanks. I didn't expect much difference in downmixing, but after testing it out, it is more different than I expected. I guess I will be keeping both 5.1 and 2.0 tracks.
I had always intended to keep the surround track, but I was not sure whether I needed to keep both the AC3 and the DTS track. After trying out though, I think that I am okay keeping just the DTS track. It may not be in spec, but as long as my software players can deal with it, it should be fine. In hindsight, I may just keep all tracks in the future, it's not like an extra 200-300MB is such a big deal nowadays.