I just replaced 3 I-drives with brand new units, the originals were only 1 year old. the only way that the openers would work is with the doors a little on the heavy side.
It's a great concept but not as reliable as it should be.
Try this link
http://www.acd-usa.com/805series.html
it is a commercial DC drive unit similar to the I drive, but is belt driven. If you go with any direct drive unit that attaches to the torsion shaft, you should make sure to include pusher springs see link
http://www.garagedoor.org/commercial...art/RS-36.html
to help the door into a vertical position as the door may not move as fast as the opener initially, and you need to keep tension on the cables.