Elgar enigma/ Picture at an exhibition

For Pictures my choices would be Szell with Cleveland, there is also an SACD version, that I have and is worth it, if your system can play them. Next would be von Karajan's

Elgar's Enigmas my favorite is Boult's others will have others. Both have many good recordings to choose from.

For Pictures at an Exhibition, you can't go wrong starting with Reiner and the Chicago Symphony Orchestra on RCA. It's one of the great performances of this work.

For the Enigma Variations, I'd recommend starting with Monteux and the London Symphony Orchestra (RCA, re-released on Decca). Also a highly regarded performance of this piece.
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thanks

$50 for Szell with Cleveland in SACD. wow pretty steep

Kudos to you for being involved in your son's music education.

Several fine recordings of Pictures as already mentioned. But, for me, to really understand this music the performance needs a Russian sensibility. The Valery Gergiev reading with the Vienna Philharmonic is hard to beat. I also encourage you to have your son listen to a recording of the music as originally composed; for piano. This will broaden his understanding. The Sviatoslav Richter recordings are very fine.

The price has gone up I didn't pay anywhere near that for it.