Here's what I find a tad ironic: all of the 'big' recordings of M2 from Vienna have been made in the Musikverein, which is a rectangular, shoe-box shaped hall. As a result, the stage ends up rather crammed for works that require a large chorus. That's not to the mention the relatively weak and 'wheezy' sounding organ in the room (Kaplan's VPO M2 had the organ from Berlin's Philharmonie dubbed in). Large works recorded in the Musikverein often times sound rather 'boxy' and somewhat muddled (Abbado's "Gurrelieder" comes to mind).
In contrast to that, the Wiener Konzerthaus is pretty much ideal for works that require lots of instruments, large chorus and a pipe organ. Bernstein's Vienna M8 that is out on dvd was recorded there (1975). Better still, is the recording that Decca made of Janacek's "Glagolitic" Mass in the Konzerthaus, with the VPO conducted by Chailly. The organ sounds fabulous, as does the choral work (since they're not all cramped up in the back). Yet, Kaplan's reduction is being recorded in that bigger hall. It might sound great if the reduction itself isn't a hindrance. Keep in mind that Avie makes very good sounding recordings.