My E5 arrived last week and I have used it regularly since then. The only other headphone amp I have is a PodRock-It, which I got on ebay for around $42/shipped. From having read the specs and the reviews here, I fully expected the E5 to blow the PodRock-It away. It didn't. At least not volume-wise. (Features-wise is another matter. There the scales definitely tip heavily towards the E5.)
I'm using a Sony NWZ-E438 as the source (although I have 2 8gb Sansa Clips), with Sennheiser PX-100's, Grado SR-60's, and/or Koss PortaPro's. And as others have posted, the output from Sony mp3 players is pretty pathetic.
When I'm using the PodRock-It and have the volume on that up to the max, I can't play the Sony beyond 20. And it's loud. With the E5 on max, I have to crank up the Sony to 27-29 (30 is the max). And while it's strong, it doesn't really drive any of the headphones I have the same way as the PodRock-It. And also, it seems like there's a little more distortion/the sound is more strained than punchy. It does, however, at least allow me to use the Sony with my favorite headphones, which is simply not possible with the Sony alone.
The E5 is a nice, small compact lightweight size. And despite what others have said about the clip, I like it. And I like the fact that you can charge it while still listening to it. Battery life seems decent, although not exceptional. And even though others have said the accompanying mini-mini IC cords are useless, I've used both the short and the longer one w/o any problems.
The bass boost is subtle. It makes some songs sound better, some songs muddy, and no big difference on others. Depending on what kind of mood I'm in, sometimes I have it on, other times not.
I'm waiting for an XM4 that I won on ebay, and given all the features on that amp, I'm expecting it to be better than either the E5 or the PodRock-It. I'll report back after it's burned in and I have a chance to put it through its paces.
UPDATE (4-25-09): The XM4 arrived today. I charged it up (via the optional Li-Ion fast charging system) and have been listening to it all day. At first I kept it at the standard gain setting, with bass boost on and crossfeed off. With those settings and the XM4 set to max volume, I had to kick the Sony's volume up to around 25. Then I tried it with the XM4's 10db gain boost option engaged, and only had to set the Sony's volume to 16, and the XM4 at 75%. I know the gain is mainly designed to deal with high impedence headphones, but given the Sony's anemic output it makes sense to me to use the 10db gain option. I don't hear any increased noise floor level listening through the Koss PortaPro's or the Grado SR60's. I'm really lovin this XM4 amp.
