I haven't heard Magma, but I really love Henry Cow's Leg End. But to give it a fair chance, I'll look for it and get back.
EDIT: (about an hour and a half later...) OK, I just listened to Trilogie au Trianon 3: Mekanik Destrukiw Kommandoh. I guess that's the same album except instead of one 39min. long piece here it's separated in 8 pieces....Hmmm....very interesting....but eventually, I don't think this would appeal to me more than Henry Cow does. So, in the end, Leg End gets my vote.
Magma 1
Henry Cow 1