Ooo Ooo! Pick me pick me! I got to work with UE so I actually played with it quite a bit. It's a really cool device. It's one of those things that people dont realize they need, but it can potentially make more of a difference than even your source or amp. In a nutshell, BA drivers are highly sensitive and we as consumers these days expect to buy a product that drives everything, so they're often not optimized for driving BA drivers. For that reason, many people have noticed that their IEM may sound different when plugged into different amps or players. The line drive is what UE calls an impedance transformer, which gives the IEM a consistent impedance throughout its frequency range and removes the inconsistency in sound. Mike Dias likes to explain it as "hearing the IEM the way the manufacturer designed it to sound." For most cases, I've found that it fills out the lower end quite a bit and gives better separation to the sound. Depending on the source you use, the difference can be very drastic. On the other hand, for something like the AK240, which is pretty good at driving IEMs, the different wasn't as substantial. I feel that its one of those products people dont think about buying, and feel they dont need it. After getting to play with it all weekend and introduce it to lots of people, most of them left very impressed and its actually the only thing UE sold out on. Anyways... I hope I'm not breaking any rules here by posting this. I dont work for UE or anything and it's my honest opinion so I think it should be fine.