Then what kind of information is it you are looking for ?
I think it is fairly well agreed on that the amp module in the HiFiMan is not quite up there quality wise with the best portable amps so that could be one reason. Another reason could be that somebody simply prefers a sound signature that is different from what the build in amp gives. I don't think there are any other "portable" sources that produce the level of line-out quality that the HiFiMan does, the source part of the unit is much higher quality than the amp part. It is not for me due to size, limited capacity, short battery life and so on but it does really sound very, very good.