As a general rule of thumb, PA mixers will tend to be noisier mixers - in several ways, not just S/N ratio - than mixers designed for recording; they just don't need the same tolerances of specification on sound. You *can* use a PA mixer for recording, but I wouldn't expect results any better than what you're getting now.
You might want to look at the "two birds with one stone" the other way around; get a halfway decent recording mixer that fit's your needs, build it into a rack with a power amp or two, and let it double as your PA mixer. One of the main bands I work with does this with a Mackie VLZ Pro and a couple of amplifiers to route to their wedges as well as drive their PA stacks.
It sounds great live; we heard the distinct difference in quality on the very first gig with the new mixer. And it gives the owner an acceptable quality mixer for use back at the ranch as well.
[SIZE=1][B][COLOR=DarkSlateBlue]Glen J. Stephan,
SouthSIDE Multimedia Productions[/COLOR]
[COLOR=DarkGreen]RECORDING RESOURCES AND INFO SITE:[/COLOR]