Hey I thought I would recommend the Arcam rDAC or rPAC, both have async and are under $500. I just got the rPAC about a month ago because I needed the headphone amp. I listen to mainly acoustic music (jazz and folk). I have been listening to the rPAC with HifiMan HE-400's and I am very happy with the top-end definition. I also listen to a lot of music via Spotify at 320 kbps and I am still able to listen without cringing. Good luck!