Rutter's edition is wonderfully researched with excellent notes regarding the genesis of the piece from the original small ensemble to the more familiar full-orchestra version. In the vocal score the organ part is given in full, with the other parts given as a second keyboard part, making it handy to perform from.
I should chime in that, if you're a glutton for punishment, it is indeed possible to play all the parts (1st and 2nd kbd, as it were) in the Sanctus on the organ. You have to make ample use of "unorthodox" pedaling to get it all, but you can get it. Pretty cool that that is the case, and it is an excellent reduction as well as a clean performing edition for singers.
I did one about 40 years ago using a small string section (vls, vlas, celli, bass and harp), and alto, tenor and bass trombones instead of horns. I had very good players on the brass parts and the balance was fine. Since trombones are traditionally THE liturgical brass of choice, at least for the last 400 years, it had more gravitas than with horns. Just remember, I'm not organ centric, like most of you. I don't even play keyboards. Not using organ was like taking the training wheels off for the choir. Ever consider Luther's translation of the Bible's imagery of the Shofar into German? Did he come up with Trompetten? Nope. He came up with 'Posaunen': trombones, plural, which could easily be extrapolated to read: posaunenchor. More useless information for your sacred music options memory bank.
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