Howdy. Looks like we are in the same boat (tri-SLI, ASUS mobo). I have been looking for a good solution also, and have not found any good external solutions either. For what it is worth, this is what I have been investigating recently:
adexelec.com
This company makes PCI extenders. My idea is to raise one video card and to put a cable extension onto my bottom PCI express slot. While I would much rather extend a full PCI slot for a soundcard, on my mobo (Asus P5N-T Deluxe), the 'open' PCI slot is in the middle, and the company only vouches for a 4" cable. They do allow 15" for a PCI express extender though.
I am still doing research on solutions though. Please post anything you might find out and I will do the same!
adexelec.com
This company makes PCI extenders. My idea is to raise one video card and to put a cable extension onto my bottom PCI express slot. While I would much rather extend a full PCI slot for a soundcard, on my mobo (Asus P5N-T Deluxe), the 'open' PCI slot is in the middle, and the company only vouches for a 4" cable. They do allow 15" for a PCI express extender though.
I am still doing research on solutions though. Please post anything you might find out and I will do the same!