I am not impressed with the sound quality using the usb input. I mainly listen to the RR2150 using a SB Touch and the SQ is excellent so it is not really a problem. Still I think the RR2150 is a fine product and deserves a better dac.
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macmini (as server) -> Logitech Squeezebox -> Outlaw RR2150 -> PSB Imagine B, Beyerdynamic DT880