At first sight the engine looks simple, but it really shows, how matters on details.
I love those straight shapes with decent bevels and outstanding color combinations. The style how you made display in bottom part of pledit and the courve display in eq is very original I also like those stripes inside vol/balance/eq bars (beautiful detail!) and how you used graient color in analyzer.
The only onethink that IMHO should be slightly different are numbers.bmp - I think that some straight pixel numbers would look better.
Awesome skin in so many color mods (I know how many time it takes to make another coor mod - absolutely great work!