Everytime I crank up Melodyne, I get this "your audio interface buffer is too small," etc. Here's a screenie of my Preference settings:

 
So why am I still getting this error message? BTW, I've unchecked the Read/Write cache to see if that made a difference. Not.

You can ignore the Melodyne message. It is referring to the ASIO buffer or mixing latency setting in Preferences > Driver Settings. BTW, it looks like your machine is new enough to not require the read and write caching in the File System section.

I also doubt you need your I/O buffers that high either. In fact too high a figure can cause almost as much trouble as too low. Sonar will get fed up waiting for the buffers to fill and drop out. I'd recommend reducing them to 512 each and then try stepping up and down from there until you find the optimum for your system. there's no "one size fits all" setting, it's system dependent.

@Karl: That's probably while I'm also getting a lot of crackling noise during playback. Every time I drop one of those Antares plugins onto a track, it snaps, crackles and pops. When I export the mix, it's fine, but during playback within Sonar, fuggeddaboutit.