Lachesis: I was toying with a few PB ideas before I landed on Saffron; one of them was Carrie-Anne Moss, but she's firmly ingrained in my mind as Styx at this point. I also considered using Juliette Binoche, who I think could work, but she's always been more Hestia-ish in my brain.
Atropos: Was always Judi Dench in my head. I did actually have a look around at other PBs but nobody else even came close. Helen Mirren was briefly a possibility, but she just doesn't match up to my mental image of Atropos.
Momus: I don't know when I decided to go with Lewis Black for Momus' PB, he just seemed like the natural choice and the more I researched him the more perfect Lew seemed for the character. I never looked at any other PBs. If I had to, I'd possibly go with Richard Schiff. And then I would be forced to find excuses to use images like this.
Mania: I don't think anybody could fit her as well as Emilie Autumn. CaptainMaggot, maybe?
Chazaqiel: Actually did start off with an alt PB, sort of. A long time ago I used to play Azazel with a Paul McDermott PB, and Chaz initially showed up as one of his NPcs. He was largely the same character he is now, but I used Richard Fidler for the PB, mainly because the DAAS connection gave me a chuckle (Paul and Richard were both members of the Doug Anthony All Stars - Richard was constantly victimised by the other two). But I don't know that there's anyone who could suit Chaz as well as Frank Woodley does. I wanted a bumbling sort of character, terribly earnest and eager to please, but awkward, not overly attractive and never entirely comfortable in his own skin. Frank's great at playing those dopey, low-status characters, and he's pretty much the king of pratfalls, so. Alternate PB? I have no idea.
Doug: Chazaqiel is no Geoffrey Salter, but Doug does have a little bit of Mike Moore in him (I confess this was written after a Frontline binge). So, Rob Sitch? Or. Or! Stephen Colbert circa Strangers With Candy.
Thalia: Was always Kristen Schaal in my mind. I did really like the previous Thalia's PB, Nora Zehetner, though, and she could very easily work as an alt PB. Or I could stick with the comedian theme and go for someone like Claire Hooper.