Newsflash: Seventh Records has put four albums up on eMusic, including two Magma live albums! The two albums are Théâtre du Taur and BBC 1974 Londres, though oddly the former omits the second disc (which consists of MDK in its entirety). The other two albums include one by Simon Goubert and one by Collectif Mu, with whom I am not familiar.
Hopefully Seventh puts some more Magma up in the near future — their albums would be particularly downloader-friendly in that many consist only of a couple tracks. I would love to round out my Magma collection with some of the more obscure live albums that I have no intention to purchase at anywhere close to full price.