Hello,
You'll definitely want to employ the 'low-gain' setting on the HeadRoom TBH amp for use with highly efficient (sensitive) low-impedance ear canal headphones ... The amp's high gain setting is likely best for high-impedance designs like most full-size headphones for example but can be a bit noisy with ECHs.
Lower bitrate, highly compressed digital music files will tend to exhibit higher background noise floor issues, especially when "magnified" via a dedicated head-amp. I would suggest using principally 'LossLess' files offering improved sound quality. An iPod line-out 'dock' device that allows for analog signal output via the iPod's bottom pin-port (made by SIK.com and SendStation.com -- amongst many others!) are also highly worthwhile and will help to tamp down the rather noisy headphone jack connection from iPod to head-amp.
Cheers,
Jorge
HR Sales /Product Manager
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