Finally, I think I'm done modding my HD600. Won't touch it ever again, except for maybe to change the ear pads when they go bad?
Pushing 3-4KHz down without cutting into the higher frequencies too much or boosting bass? It seemed like a fantasy, but somehow I achieved it.
Oh, and here's a bonus: lower bass distortion. At 100Hz, the stock measurement showed 0.399% bass distortion. Modded, it's 0.169%. That's a massive improvement IMO. It's very audible, and... I must admit, I'm loving it.
So what does it entail? Just... dynamat. Lots of it. And optional front damping if you'd like to fix the FR. To me, this headphone was a bit bright at stock, so I "fixed" just that.
Will post the process and all once I'm less lazy (or once my internet allows uploading huge images...). Now to finally enjoy my music and not have to worry about missing out on much.
Edit: some photos went through so... enjoy!
Look, ma, no dust cover, nothing between ears and drivers!