Just picked up the 82CD Karajan 1970s recordings box - actually the Korean version. Many of the recordings have been specifically remastered for this release - including the Das Lied von der Erde, which I believe is the first remastering since its old Galleria incarnation. I will give it a listen tonight.
I am very impressed with the sound on other remastered CDs in the set, namely the Bruckner and Beethoven symphonies. The M5 also sounded great, though not heard that previously (or the studio M9, also in the box).
'Not too loud on the banjoes here, Herbert...' (with apologies to Eric Morecambe):