I've known about increasing the buffers for a long time. Currently I have them set to 512 which I think, if anything, is a bit on the high side. But I'll give it a try and see if increasing them will get rid of the distortion.
It may be rare, but I've also heard from a couple people that actually
decreasing this buffer on Delta cards instead can make a positive difference (only when using ASIO).
May be worth a shot.
FWIW I've found 512 to be a pretty acceptable and stable setting for the 1010 interfaces I've worked with.
Never tried these drivers on a 66 though .. we have a few 1010s but no 66 models to test on.