For Delerium, I'd dodge the newer stuff and head straight for the old
Dossier material, especially something like Spiritual Archives. Quite dark
and lovely -- reminds me of Stalker for some reason -- and samples the
first Recoil album. I don't know if it's been mentioned here, but
Cleopatra is going to reissue all of Delerium's Dossier releases, so they
should be easy to find.
As for the Autechre inquiry, I too was a little cool on Tri Repetae, but
have nothing but high praise for Chiastic Slide, so I'd say go for it.
--Seofon