Alesis USB mixer questions

I have an Alesis multimix 8 mixer that I am trying to use with Logic Express 9. I have my input set up as USB in and I have the settings in Logic set up for USB in however there is a high pitched whine when I try to record from USB in. Are there any tricks to set up these mixers for use in Logic?

I am thinking about buying a Multimix 16 for home use and was curious if anyone has had any experience with this mixer. Or if anyone has any recommendations for a different mixer. I will be using it at home mostly, but some use recording ministry related activities.

I'm using a MacBook Pro 10.6.8, 2.3 i5, 4 gb RAM. Logic Express 9.

Thanks in advance.