Hello fellow Pro Tools HD users. After months of laboring over this build (should I or shouldn't I?) I can today (jinx?) say I have a very stable and successful HD4 PCI build. I DID NOT have to make any alterations to the heat sink as outlined in freddar's incredibility helpful video. You do have to follow his guide carefully and make note of the deletions and MultiBeast info. This is a must! I was able to just use electrical tape over the last row of "teeth" on the first two (core and 1st Accel) cards and they fit tight but nicely between the heatsink ridges. The 3rd Accel card covers the Sata3 port but I pushed the card to fit the sata cable in and the 4th card goes in with no obstruction at all. I'm still in the process of checking things but I had the system up all day yesterday mixing a small but plugin filled session with no problems. I've got a UAD quad card in the (1st) PCIe x1 slot working. A GeForce 9500GT video card in the (2nd) PCIex16 slot with both DVI outputs working. THIS TOOK SOME DOING!! PCI slots 1 > 4 (3rd > 6th) are occupied by the Digidesign Core and Accel cards. The final PCIex4 slot is occupied by a Rosewill RC-230 SataIII Raid Controller card. This gives me additional Sata and e-Sata capacity. I've also put a Plextor M5M PX-256M5M mSATA SSD into the MBs m-Sata slot. So as you can see, this build is quite full and everything works nicely. I have full USB 3 speed and full SATA 3(SATA 6Gb/s) speed as far as I can tell. I'll keep you all posted if something changes.