…in Cubase itself, and not the audio interface software? I just bought the Avid ProTools Quartet for PC, which sound fantastic BTW, but for some reason it does not allow you to change buffer setting within its own IO software. This is the first audio interface I’ve owned which would not allow this. It defaults to a buffer of 64…which is great, but for larger projects I would love to go up to 128, for example. The Quartet software manual seems to suggest that one can just adjest the buffer settings inside your DAW software, but I’ve never seen this on Cubase, as it directs you to the audio interface software to do this. Any suggestions much appreciated. 
Yeah. You want this guy:
Yes, that is how I’ve ALWAYS changed buffer settings…as this takes you to your audio interface software, but my audio interface software has no way to change the buffer setting in it’s own- they expect you to do it within your DAW software. Do you see my conundrum??? Hopefully I’m missing something here. 
Ah. Weird. Avid didn’t want you to connect it to Cubase…? [emoji5]
I have an old M-Audio pci interface which had the same problem. The reason was because the M-Audio interface software (which used to sit in my Windows tray on the bottom left of the screen and could be accessed by temporarily going outside Cubase) was 32 bit, while I was running 64 bit Cubase.
Could your problem also be a bit depth mismatch?
Steve.
Let me make a wild quess. It should read “inside THE DAW software”.
EDIT: Steve has a good alternative theory.
The default 64 buffer settings actually are working well, it’s just that I would have like the CHOICE to raise the buffer settings just in case my ASIO was running heavy due to large projects. Luckily I have the newer 5930k overclocked, so I do have a lot of CPU juice.