I use c21bee. Out of the box, it sounds good enough. But I've made a quite a lot of modifications already on the filters, caps, rectification, and opamps (ditched NE5532 and LM6172 in favor of OPA2134) that it's really no longer nadc521bee and the result I believe a lot better. What I really think is a great value player is the 521i if HDCD is not important to you and you then tweak it to your preferred sonic character.