I've had the first 5 volumes (on CD) sitting on my shelf for years. When I had the chance last year to buy #7 (I think) in a shop, I didn't. Not that I'm not curious, but I find that I almost never listen to compilations. That said, I do plan to sit down properly when I have time and listen to these CDs. I'm sure it will be rewarding, but it will take some time as I want to have the booklets in hand to know who I'm listening to. I've done this once with one of them and I really liked it. I remember Kim Cascone was really good and so was Henry Pousseur, with a vintage electronic piece from the '60s, I think.
The concept behind who's featured and in what order indeed seems curious, but there certainly is an archival aspect. If I remember right, there's a piece on one volume by an Egyptian composer who basically did a musique concrete piece several years before Pierre Schaeffer's first piece in 1948 (at least this is what I've read, since I haven't listened to it yet).