Just to clarify, you are not seeing P-CAV burns/reads, CDSpeed is just mis-identifying the mode. This drive does not do P-CAV. What you are seeing is serious buffer under-runs in the drive. You should not be trying to burn with this issue, stick to 8x until you sort it out.

There's really no way to tell whether the issue is the case or the controller, except to try the drive/case on a known good controller. My Nforce-2 board will burn and read 16x on firewire with no trouble. If it's not possible for you to try it on another system, the next best option would be to try a PCI controller card.