Dark Eldar do feed off each other so they'd likely use their pain weapons if possible.
Faith Powers could be like getting direct power from Chaos, which in itself doesn't look like Warp powers. I'm talking about the blessings and mutations here.
If the biggest gates were built by the Old Ones and can't be reproduced even by the Eldar in the height of their Empire then I would suspect the Culture can't figure it out without Subliming. After all the Old Ones are/were a Sublimed race from what we can tell.