[Darryl Ramm]

Wow, great list.

How frequently do the freezes happen and is there a noticeable pattern/periodicity to them?

When you say "ride a fader" is that purely on-screen or do you have a control surface attached (even if not being used).

You have no native plugins installed at all... not even standard Pro Tools ones? So you can set #CPU in the playback engine dialog to some low number... to ensure a whole physical core is always available to Pro Tools. I'd do that to be paranoid even if you are not expecting to run any native plugins.

Can you see anything in OS X Activity Monitor when these glitches occur?.. CPU, disk, network activity etc. yes time resolution there may not let you see things, but doe anything look unusual?

Does this happen if you run Pro Tools without the HD/TDM cards and just use built-in audio as the playback engine?