I own the HD 280's as well, but I prefer my [ame="http://www.amazon.com/Sennheiser-PC-350-Gaming-Headset/dp/B0012XFDWO/ref=sr_1_1?ie=UTF8&s=videogames&qid=1249270213&sr=8-1"]PC 350[/ame] headset for many reasons. The HD 280's are studio monitor headphones which are very flat sounding (especially lacking bass), they represent exactly what the source transmits; unlike the PC 350, they don't have directional drivers for positional audio (which helps you hear spies de-cloak behind you), nor do they have a very high quality built-in mic. All this said, I am not really a fan of the sound quality of the PC 350 and I had to mod them to get them to really come alive. If you don't mind sacrificing sound for practicability, the PC 350 are a very good gaming headset.
The best sound comes from standalone headphones, for that I recommend the [ame="http://www.amazon.com/Sennheiser-HD555-HD-555-Audiophile-Headphones/dp/B0001FTVDQ/ref=sr_1_1?ie=UTF8&s=electronics&qid=1249270574&sr=8-1"]HD 555[/ame] and [ame="http://www.amazon.com/Sennheiser-HD595-HD-595-Premier-Headphone/dp/B0001FTVE0/ref=sr_1_1?ie=UTF8&s=electronics&qid=1249270591&sr=1-1"]HD 595[/ame] which use the same positional audio driver as the PC 350, or the[ame="http://www.amazon.com/Denon-AHD1001K-On-Ear-Headphones-Black/dp/B000UPBQQC/ref=sr_1_1?ie=UTF8&s=electronics&qid=1249270609&sr=1-1"]Denon D1001K[/ame] which are closed headphones that will seal out background noise. The HD 280 are good headphones, but for a slightly higher price there are much better options out there.
I don't really recommend desktop mics because they tend echo when you use them in-game, especially with speakers being used as the output source. The [ame="http://www.amazon.com/Zalman-Microphone-Zm-Mic1-Sensitivity-Headphone/dp/B00029MTMQ/ref=sr_1_1?ie=UTF8&s=electronics&qid=1249271266&sr=1-1"]Zalman clip-on mic[/ame] would be a good choice, it's cheap, has decent sound quality, and does a good job of blocking out background noise.
I'm envious, those are great speakers. I couldn't fit the Z-2300's sub in my room so I went with its little brother, the Z4.