Well, Week, I too LOVE multichannel classical recordings. I've loved classical and large-scale film music for about 35 years now. I'm an unabashed Romantic whose favorite composer is indeed Mahler, with guys like Rachmaninoff, Tchaikovsky, and Richard Strauss not far behind.
One of the reasons I love MC classical recordings is that FINALLY it sounds as if the engineers set up 5 microfones, set balances once, and recorded the music without constantly screwing around with the mic levels! The recordings sound like real orchestras in real spaces, usually concert halls. I LOVE IT!!!!!!!!!!!!!
A piece of music you might really like is the Alpine Symphony of Richard Strauss. My SACD has Christian Thielemann conducting the Vienna Philharmonic Orchestra, one of the world's finest orchestras for decades. It's DG 471 638-2. Another fave of mine is Telarc's release of Jerry Goldsmith conducting his own movie music. It's not 'classical', but it's close. Philips recorded this for Telarc, in 2001 I believe. Goldsmith and the LSO were really 'on' for these recordings in EMI's big Abbey Rd. studio. The bass drum in the opening 'Star Trek' suite (and thruout the music) sounds fabulous; this may be my favorite MC recording. Telarc SACD-60433.
If you like the piano music of Johannes Brahms, probably you'll like his 1st symphony. A wonderful MC recording of that is by Marin Alsop and the LSO; on NAXOS DVD-A 5.110077.
Personally, I prefer the sounds of DVD-A to SACD, as the latter tend to have MUCH higher noise floors than DVD-As, but SACDs are much more common, not that they're common at all.
Live it up; there are hundreds out there.