Thinking of getting Astro Mixamp & Sennheiser PC 350

I'm thinking of upgrading my audio solutions for gaming. I want to be able to have only one headset between both my Xbox 360 and my PC. Simulated Surround Sound is a plus and high fidelity quality is a must. Currently for my PC I have a Cyber Acoustics AC-401 but today I broke the mic jack tripping over the cable, really don't want to buy a new mic just because of that (even though they only cost $14.50). For my Xbox 360 I use Turtle Beach X4s. I'd actually prefer to go wired, alleviating the issues of static and batteries. I used to own Sennheiser HD 555 audiophile headphones. Never heard better quality speakers before in my life. I'm thinking of getting a Mixamp so I can use the headphones on my Xbox and get simulated surround sound (like my Turtle Beaches) for both my PC and Xbox 360. I know the only thing I'd lose that'd suck is the voice monitoring.

Anyone have any opinions they'd like to offer on the Astro Mixamp or Sennheiser cans? Thank you!