I've always had problems with cable select. Either it doesn't work or it doesn't work.
When I was cobbling together my own PC about a month ago, I thought I would set everything to cable select and let the PC sort it out. No dice. The first HD would work and the second wouldn't show up, One CD-ROM would show up and the other wouldn't or a problem combining the two. So, I just set everything back to Master/Slave and the problem disappeared.
I can't say that's the solution to your problem, but I thought I'd share.