mac/echo/cubase driver problem

I've just changed platforms to a mac pro, OS 10.6, 266mhz, 6G ram, quad xeon,and am using an echo audiofire 4 as my interface. After twenty minutes or so, audio starts to break up, progressively getting worse. It can clear sometimes after I mess with the buffer, or re-choose the echo driver, or change the sampling rate back and forth between 44.1 and 48k .If i go to the internet with a music file open, it is often silenced when I return to it. Often I must close the file altogether.
I'm new to mac and am sure I've overlooked something.For instance, is there a setting somewhere deep in mac that is specifying a sample rate of 44.1k and interacting with my audio driver? Any insight would be much appreciated! Bob

Definitely sounds like a driver related issue. I assume you have the latest driver and that your interface is compatible with the mac?

Thanks,Blairtechguy!I've updated the Mac OS, and downloaded fresh Echo drivers,including a previous edition,to no avail. It seems that the Echo drivers are considered excellent,so I still suspect it is my unfamiliarity with the mac. Do other apps such as itunes specify sample rates on a page I can't seem to find? Because audio starts out intact and then disintegrates,makes me wonder if it is a thermal problem with the interface,though I've never heard of that. Bob