gonk,
The manual may be a little misleading there (they say "mode can produce the rear surround information from a 5.1 source" --
Try this quote from DTS Online: DTS Neo:6 also decodes a center-surround channel from Extended Surround matrix soundtracks.
I think both those quotes are referring to something other than 2-channel sources; they're talking about extracting the surround back channel from properly encoded DTS-ES Matrix mixes (ES = Extended Surround), which are technically 5.1 discrete channels, as opposed to DTS-ES Discrete mixes which are true 6.1.
When the surround back channel was first introduced to home theatres, both THX Surround EX and DTS-ES Matrix used Dolby Pro Logic decoding to extract the additional surround channel that had been matrixed in. Since then, some things have changed: THX Surround EX still uses Pro Logic, but DTS has mandated that their Neo:6 decoding be used on ES-Matrix encoded soundtracks, and licensees of Dolby Digital EX are allowed to use either old Pro Logic or PL II (I think most manufactureres are using the latter, at least I hope they are).
Having said that, I agree with you that the wording of the Neo:6 descriptions are confusing; both in the Outlaw manual and at DTS Online.
Best,
Sanjay