I/O issues?

I've just completed my first build and I'm having some very odd problems.
Components (all new):

CPU: Intel i7-2600
Mobo: MSI P67A-GD53 (B3)
GFX: XFX Radeon HD 6870
16Gb Crucial Ballistix memory
Intel 520 SSD (128Gb)

WD 2TB Hard drive
LG Blue-ray drive + Sony OptiArc DVD Drive

I've been having real trouble reading DVDs - on either of my new drives, and on a variety of media.  This includes Windows and Ubuntu install disks, so the problem occurs before an OS has been loaded.  I even had the same troubles on an external USB drive.

The Windows install would BSOD, the ubuntu drive complains of I/O issues.

At one point I managed to install Windows 7 from a USB stick, but had similar issues installing software.  For example, The MS Office 'default install' managed to work, but there was a consistent problem reading a file during the 'custom install' - it would complain of disc read issues, and stop.

I've just now finished trying a bootable Ubuntu USB stick - I couldn't install from this (I/O issues), and the 'try without installing' feature set up an OS, but it was very instable ('disk errors').

I've tried 3 different DVD drives now, 2 internal and one external.  I've tried my SSD, and HDD alternately.  I've tried various RAM configurations, and 2 days of Memtest on the RAM succeeded without errors.  I've tried all the BIOS settings available (very few), and tried updating / downgrading the motherboard firmware.  With Windows installed, I tried various driver updates.

I convinced myself it was a problem with the motherboard, and so RMA-ed it, but the replacement has exactly the same issues.

By process of elimination, I guess the problem must be with the processor, but I don't understand why.  Does this sound reasonable - has anyone seen anything like this before, or can anyone imagine what the problem might be?

Or can anyone suggest some tests I can run to show that the processor really is at fault before I ask for a replacement?