If you haven't seen / heard these already, you gotta check them out. Pro pianist Iain Farrington masterfully arranged Mahler's symphonies for
solo piano and performed / recorded them for YouTube videos with scrolling score. So far, he has uploaded all of M1,
Blumine, movements I-III, and VI of M3, movements I-III of M4, all of M5, all of M6, and all of M7 (with his latest video from a month ago). I'm assuming he will finish the set at some point. It's interesting that there are absolutely no vocal related works or movements uploaded. Yet?
https://www.youtube.com/user/iainfarrington/videosI particularly like the arrangements to the M5 and M7 finales.
Disclaimer: I'm not a pianist, but these seem EXTREMELY difficult.