I have asked about this and the reply was 'it's fine the way it is'. He told me none of the documentaries that he distributes have a 5.1 mix and for gritty fiction drama's the use of surround sound will do little to support the film. Because of it's documentary-like realism we can swing it I guess.
What's in the surround speakers isn't the problem. The problem is the lack of a centre position with stereo. This has always been the problem and why stereo has never been a theatrical sound format. I explained the problem in
this thread. Also, I'm not sure what documentaries the distributor is distributing. Even for lowly old TV, 5.1 audio is the delivery requirement these days for pretty much all the networks.
EDIT: It's common knowledge in theatrical circles that Stereo is the worst of all audio formats for theatrical playback (which is why it's not supported), after your last post though a re-think is required because 2.1 audio would be even worse! Fortunately though, even more than with 2 channel stereo, there is no way to distribute a 2.1 mix to a cinema!
There is at least one cinema in my area that I'm aware of (there are likely to be more) that can project from a Bluray that does 4 wall deals with local producers to showcase their movies. It is a small cinema, with two screens. One being able to project in 35mm film, the other projector being digital able to project from the Bluray and I'd assume DCP.
So the question probably would be, do all cinemas have a 5.1 mix as the minimum requirements for sound? If not, that'd reduce the cost/time required considerably. Releases that aren't wide don't need every cinema chain to be able to accept their movie.
35mm film has two optical audio channels so could in theory contain a 2 channel stereo mix but these two channels are always used to contain an LtRt (4.0) mix, so putting a 2 channel stereo mix on 35mm film is likely to cause problems, as will feeding a 2 channel stereo mix through a cinema sound system, as CrackerFunk discovered to his detriment and discussed in
this thread. To avoid the inherent problem of stereo or of accidental decoding issues, the DCP specification requires a minimum of 3 channels of audio (L, C, R).
As 35mm film and DCP are the only viable distribution formats for theatrical release (and neither of them support 2 channel stereo) I don't see how a distributor could distribute anything with just a stereo sound mix, let alone would want to (baring in mind the first thread I linked to above). The exception I suppose, would be if the distributor had access to a network of cinemas like the one which Sweetie describes. But, the overwhelming majority of cinemas can only play 35mm film or DCP and the odd tiny place which figures out how to connect a BluRay player to their projection system is likely to exhibit the same problems which ruined Cracker's screening.
In practice, even for limited theatrical release, 5.1 has been the minimum requirement for about 15 years or so, while the bigger films on wide release have 7.1 mixes or use one of the new audio formats like Dolby Atmos. If a distributor is willing to try and theatrically distribute a film with just a stereo soundtrack they just probably don't know what they are doing! Unless, they have connections with those few cinemas who have jerry-rigged their systems to play stereo soundtracks and those cinemas have patrons who don't mind watching films where the sound only appears to be coming out of one speaker at the far edge of the screen.
G