Hmm. So it comes down to.. The convenience of portability vs. the availability of Dolby Headphone.
I just checked and it seems my motherboard (Gigabyte EX58-UD5) has Dolby Headphone built-in (well, available in an update). That sure complicates things. Decisions, decisions. At least now I know it's going to be one of these two solutions. Three hours ago I was blind.
You could throw more money at the problem and get an Audio-Technica AD700 for gaming. Plug it straight into your motherboard, it's easy to drive.
That said, I don't think your motherboard actually supports Dolby Headphone. The Gigabyte website says Dolby Home Theater. Dolby Headphone is a surround sound emulator, that allows downmixing of 5.1 or 7.1 channel audio into two channels while maintaining directional sound.
I suppose it comes down to this: How often do you see yourself gaming, and how often do you see the need for (trans)portability? Both options are good and cost about the same, so prioritize their strengths.
Edited by Head Injury - 9/30/11 at 7:25pm