Are there any portable players out there that also have the option of operating as a mobile DAC/AMP unit? Like, instead of just using their micro USB jack for charging, they can also accept a USB audio signal if present and pass it to their own internal DAC/AMP hardware? Maybe there's a switch on the side to change between the two operation modes, maybe it's automatic, I dunno.
I'd like a portable player that I also have the option of plugging into my phone or tablet and using its quality digital audio conversion and amplification just like it was a cheaper dedicated DAC/AMP unit. Would be nice not to have to own two separate devices to accomplish this. Is there even anything on the market that does this yet? I assume there must be, because it'd be a pretty convenient feature and easy to add, but I haven't heard of anything as yet.