As it happens I have the Prang, and I even bought them to use with the Ikwen, but once I had both ranges to compare side-by-side, they turned out to be too different in sculpting style to be compatible by my standards. I don’t just mean different like different races in the same sci-fi setting, but like different settings rendered in different artistic styles. They look like different scales, too, mainly because of the sizes of the guns and other equipment (the Ikwen are more 15mm, the Prang more 18mm). I’ll still use the Prang with my Ion Age figures, but they won’t be sharing a setting with the Ikwen. Good thing I like gaming numerous sci-fi settings even in the same nominal scale.
The Crusties might work if I stick to the ones in hostile environment suits (the naked ones don’t really make for enough of a contrast with the Ikwen, thematically). The Kra’Vak strike me as a “warrior race”, but I’ll keep contemplating them to see if I can get over my preconceptions of them. The Ixx look a bit too “wicked” for the role, although I do like the non-humanoid anatomy.
I do intend for the colonialists to have robots and drones, but I still want some living grunts as well.
Thanks for the suggestions so far!