I'll start this review with the most important information--these bad boys retail for about $150 US for the headphones and the transmitter unit. If you shop around a little online, you can find them a tad cheaper.
Amazon.com sells them for $147.99 with free shipping.
If you're willing to plunk down about a hundred and fifty smackers for premium 5.1 audio, you can't do better than these comfortable, fully digital, wireless headphones.
Setup is quick and easy. You plug in the AC adapter, put the included AAA batteries into the headset, then connect the unit to your console.
The Ear Force X4 comes with a TOSLINK cable, aka digital optical. This is basically a fiber optic that plugs into whichever AV cable you are using on your console (all the standard ones are supported--Component HD, VGA HD, S-Video and SCART) and delivers the highest quality audio signal.
The transmitter unit base also includes an optical out line so you can run it to your usual setup/receiver. This allows you to listen to games on your headphones and regular speakers at the same time, a neat feature.
The base unit also includes analog out ports (the red & white RCA jacks) if you want to connect it to a television.
The analog outs turn off when the digital optical is in use, and the digital does the same wen the analog is in use. This means that if you have it hooked up and want to watch TV after you are done gaming, you can do so without switching a single wire.
The X4 unit fully supports Dolby Digital 5.1 and Pro Logic II decoding, which means even though they are technically stereo headphones, the signal from your console is processed and delivers a 5.1 channel audio field in your noggin.
Game-wise, in Dead Space, small clanks and clatters rang true, and necromorphs couldn't sneak behind me anymore. In Gears of War 2's Tyro Station, I could hear the rumble of the train before I could see it, and its sound would blow behind me from right to left even as huge Boomers stomped around to the front-left of me.
Movie-wise, DVD audio has never sounded better. Dialog comes through sounding close and crisp in the simulated "center channel" even as sound effects take up the left and right and the bass rumbles beneath it all.
Music-wise, these headphones deliver pristine sound. Even the heaviest, busiest symphonic metal sounded clear and powerful, and the large padded cups manage to cut out background noise so you can hear small nuances very well. The headphones' frequency response is 20Hz - 20kHz, with "oversized" 50mm speakers that deliver defined low end.
The Ear Force X4 has a few features made specifically for us Xbox 360 gamers. It comes with a detachable cable that plugs in to the bottom of a controller for Live chat (note, though, that it won't fit into a chat pad). The volume of the mic/chat is independently adjustable from the main signal, and the X4 has a "chat boost" feature that will automatically increase the volume of the chat audio up to 10dB for when the game gets louder and people are still talking. You can also set the unit to monitor your own mic, so you can hear what you say/sound like.
The boom mic has a nice length and is fully adjustable, and can even be removed for when you are watching movies or playing alone.
If you have a spouse or roommate that likes to game with you, they can get just the X4 headphones and receive the signal from your transmitter, so you can both enjoy isolated 5.1 audio.
The headphones also have a slider which enables a "bass boost" of 9dB to sounds at 150Hz or lower. This gives in-game explosions a nice, powerful 'thud' and can make music sound even more full.
The X4 delivers 100% signal fidelity in a range from 4 to 30 feet, and the headphones have 4 IR receivers so you get full 360 degree reception. Aesthetically, the X4 base and headphones match the Xbox well. The transmitter unit has a metal rack to hang the 'phones on, and the headphones themselves are very light (about 9 oz) and comfortable to wear, even for extended periods.
$150 may seem like a huge price tag, but these are premium digital 5.1 wireless headphones, made specifically for the Xbox 360. Battery life is around 20 hours, although premium Lithium AAA batteries should last even longer. I give these a solid 10 because not only are they the best-sounding headphones I have ever owned, they make gaming that much better with high end audio on top of chat functionality.