BobF
ASIO interfaces usually have a separate app for setting sample rate and buffer size. For example, mine looks like this

Ah! Another US-16x08 user! Love mine! Had it for about a year, now. Got mine on an MF SDotD for $200! How's it been working for you? Also, I like the (Lifer) in your sig. Reminds me of an Army doc I had who asked my if I had plans to be a lifer (there were two different medical terms he could use to describe my situation; one was medically disabling, the other wasn't; I told him I wanted to go home; ha).
Back on topic...
When tracking, it's typically recommended to keep the audio interface's Buffer Size as small as possible (before clicks/pops/dropouts occur) for lowest latency. When mixing and bouncing tracks with lots of FX, it's really helpful to raise the Buffer Size significantly (like from the 128 samples shown above to 1024 or 2048). This substantially reduces the interrupt processing load on the CPU and speeds up rendering.