There is a similar record (LP) dated about 1980: look at http://www.bib-bvb.de/fachbereich/Herrenchiemsee-Bibl.pdf
bottom of page 73
english review: http://ourworld.compuserve.com/homepages/TVRC/tvrc8b.htm
Dennis NasebandKai SuzukiDer Tölzer Knabenchor 2CD set. Arnold Ostmann's live recording with the Drottningholm Court Theatre Orchestra and Chorus. Extraodinary singing by the three boys from the Tolzer Knabenchor, boy sopranos Kai Suzuki and Dennis Naseband and Boy Alto Simon Schnorr.
There is now a DVD
No, the Drottningholm DVD is not that Magic Flute ! The DVD is B000FIHZ5K from 1989, the Flute with Dennis was recorded in August 1992)