IMDB has an "alternate versions" link for the movies. They aren't always accurate, but they're pretty good about versions.
ST I, TMP, only had the Director's Edition DVD release.
But the HD version, that I downloaded, appears to be the theatrical version. However, Neil S. Bulk had read that there was some color-correction, because it was made from the digital master that sourced the DVD re-version. I haven't done a shot-by-shot comparison to my LD, yet. I once publicly stated my desire to, perhaps, someday, convert it to DVD, as well as reconstruct the extended version. Unfortunatally, that would be months or years away, if ever. Maybe someone else? I could send them the HD files.
IMDB seems to say that the 1st DVD release, of ST II, is the theatrical version, if I read it correctly.
Also, according to them, both DVD versions of III, IV, V, VII (Generations), VIII (FC), IX (Insurrection), and the widescreen version of X (Nemesis) were the theatrical. (Excepting the Fullscreen Nemesis DVD - which was cropped to Fullscreen).
And IMDB says that none of the released versions of ST VI match the Theatrical scenes, exactly. Even the Laserdisc & VHS versions.
I suspect the HD version, that I downloaded, matches what they list for the theatrical scenes, but I haven't checked it scene-by-scene.
For Aspect Ratio purists, you can't get ST6 in the Theatrical aspect ratio, which IMDB says was 2.31:1. (As far as I know). But at least you will be seing more of the picture, than was in the theater.
ST6 was shot full-frame (Super 35). Both DVD's have the matte opened, significantly. So does the HD that I downloaded. Star Trek films on VideoDisc says all the Widescreen Laserdiscs are 2.1:1. IMDB says 2.1:1 on its alternate versions page, but says 2.35:1 on its Laserdisc specs page. Either way, I didn't get the widescreen LD, yet, so I can't vouch for either claim.
I do have the fullscreen LD, with the matte opened up father - but, like most open-mattes, it's zoomed in far more than seems nessecary - we still don't see the whole picture. I'd love to see a good conversion of that.
They also claim 2.35:1 for all the movies in some of the collections. But that's unlikely.
The director supervised the opening of the matte, for the Collector's Edition. The first DVD's playback looks a little squished, horizontally, to me.
The ST6 HD version, that I got, is roughly 2.01:1, but I suspect it may have been released to theaters, that way, to be "soft matted" by the projector. So it could be possible to crop it and get what we saw in the theaters - but there'd be no way to verify it.
(The DVDs measure out to roughly 1.95:1 for the first, and 1.98 for the second, by the way. I say roughly because I didn't crop every pixel of black off of each edge).