The new Duet is really two products in one: the new display-less Squeezebox Receiver and the new Squeezebox Controller (a wifi-enabled remote with colour LCD that works with all Logitech players).
When used with an external DAC the performance of the SB3 and the SBR is identical. Apparently they have the same digital out circuits and have been measured to have *exactly* the same jitter.
A lot of people seem to have great results with an SB3 (or equally SBR) and external DAC e.g. Benchmark, Lavry etc. If you are intending to use the SB3 or SBR specifically as stand-alone I recommend you visit logitech.com to read their specs carefully to see which one suits you (they are not the same).
Darren