If I had to do it in order, I would probably go like this:
Arcturus - The Sham Mirrors (2002)
Green Carnation - Light of Day, Day of Darkness (2001)
Peccatum - Lost in Reverie (2004)
Sigh - Imaginary Sonicscape (2001)
Diablo Swing Orchestra - Sing-Along Songs for the Damned and Delirious (2009)
Mr. Bungle - California (1999)
Vintersorg - The Focusing Blur (2004)
Stolen Babies - There Be Squabbles Ahead (2004)
Solefald - In Harmonia Universali (2003)
Meshuggah - Destroy, Erase, Improve (1995)
I think that would be a good order for Dayvan Cowboy to follow as I don't know how familiar she is with the guttural vocals found in more extreme metals. It can be very hard to get into, especially for women I find (I'm not saying EVERY woman, just some). Meshuggah might do something for you, but it might not, it's very chaotic, but Jens Kidman does some of the best guttural vocals in metal.
As for you duga, I think you could go in at any album and be fine, but kudos for already knowing Sigh. I also remeraber introducing some metalheaRAB to Sigh via Imaginary Sonicscape and a few joints, definitely earned some cookie points because these were some of real metalheaRAB.
Let me know if you need help procuring the album.