I tried a few things without Kontakt.
buffers = 64 is still funny. Different songs are different. Sometimes there is a feedback loop where the meters are pegged and it whines, sometimes it's silent and sometimes it's just crackly. Sometimes it's silent when you load something in SONAR, then changes (for the better) if you change the buffer or offset - while everything is loaded.
buffers - 32 is definitely not worse. If anything it's more consistent, and just crackles (it doesn't do the silence or feedback howls)
Maybe it all depends on the combination of buffers and offset. I know with the older driver and using the windows app - it wouldn't let you do certain combinations without a warning.
Nothing works reliably until I go to 128 buffers and 48 offset. That's 8ms RTL in SONAR (it used to be 7.8ms with the old driver) and is workable - so I stick with that.
I'll play with this every once in a while - but it gets boring (especially after rebooting dozens of times recently while testing this newest driver) and I'd rather just get on with playing than troubleshooting all the time ;-)