I had the PC350 for a while, paired with the more upscale Xonar Xense.
The PC350 is "meh" at best. Sound doesn't isolate particularly well, inconsistent bass (weaker then I like at least), and flat out not as good as cheaper headphones I've head. They'd be a decent buy at under $100, but I really can't recommend spending much more then that on them.
That being said, they "do" require a bit of time to burn in, so after several dozen hours, they should loosen up a little. Also make sure you are using the DGX's amp, as that should help properly drive the headset.http://www.head-fi.org/t/461785/an-in-depth-headset-round-up-review-turtle-beach-hpx-astro-a40-sennhieser-pc-350