Also, anyone know a good mod to make the 650s into a closed can?
I would also suggest looking into a decent pair of iem's. I looked long and far for my pair and thought that because of my ear canal shape that I'd never get a pair to fit. Well, I finally did...the vsonic gr07. The sound signature is a little closer to the hd600 than to the hd650 but I'd still say that it's in the Senn ballpark.
I use a Sansa clip zip with mine and feel like I have some seriously audio quality when I listen away from home. They cost just under $150 with free shipping.