As I write I'm listening to a nice recording of Rachamninov's Vespers, Op. 37, done by the Academy of Choral Art in Moscow with Victor Popov conducting. For my money, it's his most characteristically Russian-sounding music. Of course my idea of what is characteristically Russian was influenced early -- I was probably 17 when I got the record -- by an album of Russian liturgical music, sung, I believe, by a Russian exile choir in Germany. I fell in love with that music, with its impossibly low basses helping to create the impression that the music was growing right out of the ground -- the Russian soil -- and enveloping you in sanctity of a very earthy, perhaps primitive kind (gosh, it's hard to describe music in mere words!). I loved Tchaikovsky early too, but in retrospect I think he was more in tune with western European influences than composers like Moussorgsky, Glinka, Borodin, even Ippolitov-Ivanov, who sounded more "really Russian" to me. I see Prokofiev as very Russian too, but in a different more modern way.
Rachmaninov loved that music too, and the Vespers is a conscious attempt to put its spirit in a slightly more formal, perhaps arty form. His better-known music -- the piano concertos mainly but also the symphonies -- seem a bit more elaborately classical and a bit westernized, which may have turned out to be his true voice.
The Temecula Vintage Singers did the piece the year before I joined them, so I've never had a chance to sing it. It sounds as if it would be fun -- challenging, but fun.