Much as on must admire the effort taken by the arrangers, I cannot help but wonder why? Mahler was such an orchestral composer that any reduction, let alone piano reduction would turn the music into, indeed, black and white as opposed to the opulent colo(u)rs of the original, colo(u)rs that are essential to the musical message in Mahler. (That said, I was not so long ago at a concert which featured Das Lied von der Erde in chamber-orchestra reduction, which was rather nice. But Das Lied is the most chamber-like symphony among the lot).
All that said, I've been messing around lately with another great symphonist's unfinished 11th Symphony, namely Bruckner; more precise the various completions thereof (6 so far, by 4 completors!). Now here is a composer whose symphonies might work on a keyboard instrument, meaning the organ. Anyone know if there are (recordings of) organ transcriptions of any Bruckner Symphony?
all best,
gep