* The beyerdynamic DT660 and DT880 appear twice in the Build A Graph drop-down. These probably represent different editions (e.g. 2003 and 2005 or 2006), but it isn't listed clearly.
* A Reset button on the Build A Graph page would be nice. The lack of one isn't a mistake as such, but a Reset button is pretty much a standard feature on pages like this.
* When I do a Google search for headroom desktop portable, the first hit is for a bag, and the second hit is for a Headroom Desktop Portable product page that no longer exists (and Google's cache reveals outdated pricing and options). You might want to consider redirecting the old page to the "2007 HeadRoom Portable Desktop Amp" page.
[edit: I see that the #1 search result for headroom desktop portable on both yahoo.com and live.com and the #2 hit at ask.com are for the same defunct page, which by the way reads, "The page your are trying to view has been moved or is no longer available."]
* There are dead links on your Reviews and Opinions page. There might be others, but the OCWizard review page is gone, and older Stereophile links take you to the Stereophile home page.