The new release looks pretty good to me!
I downloaded an MP3 sample from the Warp page in the hopes that it’d have more details, but it didn’t include an ID3 tag. I didn’t see any clues in other digital stores (Bleep, Apple), either. The Wayback Machine first archived the Bleep page in 2014, but that’s no guarantee that it didn’t exist earlier. I also tried checking the iTunes UPC database, but https://itunes.apple.com/lookup?upc=724384831226 (that’s the French CD release’s UPC) unsurprisingly lists the 1999 release date.
Unless someone else knows a trick for convincing any of these digital stores to cough up the date when the release was first made available, I think I’d just leave it blank in MB. It looks like the Discogs digital release doesn’t include a date either.
2x9 seems reasonable to me – that’s how both Warp and Bleep present the digital downloads.
Edit: The Medium documentation agrees:
Digital (as opposed to physical) releases don’t have “real” mediums, but they should be entered as several mediums if they are officially divided in several “discs”.