I appreciate and understand the basis for the superiority of a dedicated, purpose-built DAC vs. that generally found in laptops, DAPs, phones, etc. However, I'm unclear as to the real value in adding a nice (dedicated) external DAC to something like a DAP or iPhone/iPod. Once the signal leaves the player, isn't it too late for the external DAC to make much difference before passing it onto the amp?
I'm talking about running an iPhone5, iPod 5.5, iRiver H340, Windows PC and/or MacBook as the source (primarily VBR MP3 files) to a dedicated headphone amp (MAD Ear+ HD) and then to a pair of Grado RS-1i's. There seems to be an implication that a good external DAC can "fix" the sound produced by the typically inferior internal DACs of most DAPs, basic CD players, etc. Is this really the case? I'm especially interested in this as it concerns portable DAPs like iPhone/iPod, iRiver H340...because, I've also considered purchasing another DAP in this market (i.e., iPod Classic 7th gen 160GB, iBasso DX50...).
Just trying to understand how much emphasis can be reasonably placed on the value of a good external DAC when placing it between the player and the headphone amp.
Any thoughts/opinions would be greatly appreciated!