Mike, I'd second the points made by Mike Richey; unless you're talking about extensive behind-wall work which you're not experienced in, a professional installer might not be necessary. While he may be quite competent with the physical details of an installation, it's possible that he's a bit short in his knowledge of audio technology; for example, how loud you'll play it has little or nothing to do with the gauge of the wire. An excellent discussion of speaker wire, with suggested gauges, by a well-respected veteran audio professional is found
here and might be of interest to you.
