I absolutely love Ash On Dust, I've listened to the song you linked, the whole album, great pieces for coding software in the late evening :-)
Also, since I listened to the single on youtube, it automatically loaded this piece at the end:

I don't think it could be categorized as alternative or progressive, as I think it tends more to the classical. However, it seriously made me remember the Tristram music that played in the Diablo game. I know you've gamed some, but not sure if you've stopped before Diablo came out or after, but that's a beautiful song, please check it out.