I recently tried Vita's headphone out.
I had read somewhere it was not good, but it was surprisingly good. So much that I am considering loading some songs on it.
To test it, I initially used you tube hi res version songs. I plugged in Hifiman RE400 which can get quiet harsh with my cellphone.
to my surprise, sound was quiet refined and smooth. What surprised me the most was soundstage depth. Instrument separation was also stellar.
Although it was not perfect. Instrument placement was not very precise and was rather hazy. Also note level detail was not very clear or pronounced. Although how much is because of youtube, I don't know.
But it offered a very refined sound, and I think for me is a legit portable music player.