I have the 6xx paired with a xduoo ta-03s with upgraded tubes. This was end game for me. Music through this setup literally gives me a euphoric feeling in the same aspect a psychedelic mushroom can. Not near the intensity of a psychedelic obviously but small subtle hints of euphoria surging through my stomach and body. Like 1/100th of the euphoria psychedelics can give you, but still enough to notice and feel great from the blissful inviting warmth of the music