I agree the symphony metaphor is a good one as APA is generally balanced. The style is really variable. I classify APA as classic, or old school, and new school. In the classic/old school category are beers such as Sierra Nevada, Boulevard and Boston Lager (I know it's a lager). In the new school category are Dale's Pale Ale, Odell 5 Barrel and Great Divide Denver Pale Ale. The new APA has more hop aroma and flavor but has the malt to back it up so it is still balanced. I also see some similarity to an amber ale as the three I mentioned as new school have some slight caramel character.
My favorite APA recipe is based off one from Basic Brewing Video. I use 90% 2-Row and 10% C-60. It is all late hopped with 2oz. each of Simcoe, Amarillo and Cascade at 15, 5 and flameout respectively. I've made this beer about 6 times and love it. I may try swapping some Munich for the 2-Row at some point. I usually ferment it with Chico but used Pacman a few weeks ago and it subdued the hop flavor. It came out tasting more like SN than the more assertive pale ale I prefer. I will always use Chico on it in the future.
Edit: I just looked on the Odell and Great Divide websites and those have won awards as English Pales. DPA is even labeled as such. I don't get it at all. I get more hop aroma from those than I do many other APAs. This style is confusing.