I've owned a N20 for almost one year now and I can honestly say it's the best source component I've ever had, both digital and analogue. It's very slightly bettered by the N30 by a very small margin, not worth paying double the price.
I've never demoed the W20SE or the N200.
It's real strength is having a master/word clock input which really elevates its performance amongst it's peers.
Aurender's literature states that AES/EBU is the best sounding output but I must disagree. The USB with external clock is far superior even though an external clock isn't supposed to help USB - go figure. Only USB or I2s will play native DSD.
I need to buy another streamer but it's difficult accepting anything less than the N20 and I know the external clock has a big part to play.
The N20 is THE total package this side of $20k.