Received my E11 today, and I can confirm that if you have the gain on High and Equaliser set to preset 2, on my IE7's the bass becomes a bit too overpowering but nowhere near distortion. A/b'd the HD448 just now against my 438 stock without the E11, if you use Gain on Low and Equaliser Preset 2, the sound is quite good and punchy quite similar to the stock HD438's (mine are completely modded to another level) or you can use the High gain for bit of a boost in overall frequencies which increases the soundstage quite a bit but with a recommended Equaliser preset of 0 or 1 (max on 2 or 1 for some songs and you lose control of the bass and overwhelmes the rest of the sound).
For $75 that I paid for my E11 is pretty good value for such a portable amp and it sound(surprised when I received it earlier today due to the size), but it nowhere near compares to my Graham Slee Voyager or my other two DIY tube amps (including a modified 12AU7 tube amp off ebay), going to leave these on for the night out of my Droid X letting it burn-in, hoping my friend doesn't break anything of my Zune combo I let her borrow while she is on a little vacation with it
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