wonderful story! the Bachianas Brasileiras is indeed astonishingly atmospheric, among the modern recordings I like Barbara Hendricks on EMI for purity, though Kiri Te Kananwa once did a great version too. I would also try layering sounds mixing a little of the soprano soloist with the female ah. You could edit so that after-touch pressure brought in more of the soprano vibrato loop on long notes just where you wanted to trigger it for a little distinction in the sound.

I still have a lp of the Rachmaninov Paganini variations by the New Philharmonia somewhere because after searching though many, many recordings never found another with such a sweep on the 18th variation to make the hairs on the back of your head stand on end. I really must digitise that recording one day so it is safe from the ravages of time. Ashkenazy and Haitink on Decca (London in the States) probably came the closest. Try also the second symphony and symphonic dances, which really were the fourth symphony. There is a human melancholy in Rachmaninov of the refugee who lost his homeland for ever. It is said he was one of the finest pianists of his time with huge hands able to span C to oct A and play C E G C E - phew!