The King's Singers, I think. At least, I have a record of them doing that kind of numbers. The problem is, they are six highly trained professionals, while we are 30+ amateurs, most of whom are elderly, can't read music, and can't pronounce English to save their lives (French, Latin, Spanish and all flavours of Occitan, no problem, Italian with a tad more effort, German, painfully. English, very badly), and we only practice 2 hours a week.