Thank you ourfpshero! This mod really does work, I mean REALLY. I drilled 11 smallish holes into the plastic inner casing, first on the right-side earpiece only, to compare the difference with a few bass-left/right-equalized tracks ... and boy was there a difference!
I modded the other earpiece too, and then tested, nice bass, there's really a lot of more oompf to these cans with such a neat little mod. Then I wanted to control the bass a bit more, it was maybe a tad too much colored. I stuffed the cans with clothing filler wool, and that really did the trick, more control, no overblown flapping. After a while, I found myself wanting a bit of air, the pleather earpads isolate so much that the renewed bass started to feel a bit overpowering. So I fetched a pair of HD 595 velour pads, and they're a perfect fit, easing the flow of the lows, giving a fresh breath of HD 595-like feel to the PC 350.
So yeah, I am very very happy with this mod, the wool and the 595 pads, my PC 350 have never sounded so awesome! They're now what closed 595's should sound like IMHO
So a little advice? I've heard 1 hole, 3, 11, cotton/wool, no cotton or wool.... I dont find the PC 350 horrible but my comparisons are turtle beach hpx and senn hd280's. They have their pros and cons to both. I find the bass to be lacking of course but also think that its not quite as tight as the 280's. Also i find the highs can get ear piercing in modern warfare 2. Would a good place to start be one hole and some cotton or maybe other damping material?