Most music looks more like noise rather that a single tone. While single and 2-tone tests are important ways to measure systems, probably a Noise-Power-Ratio (NPR) test will give you your max gain setting. It's somewhat complicated to run, but it will give you the truest setting.

Definitely agree with the previous posts though: impedance will vary as a function of frequency, so speakers react differently at different freqs. I've been meaning to download some test tones into my RIO for this very purpose. Better yet, how about a test tone routine embedded in hijack???

-ted