I have not tested N20’s USB or SPDIF outputs when N20 is being slaved to external clock. Since my DAC is a Network Attached DAC, the recommended configuration by the manufacturer is through RAVENNA network. In this configuration, I did hear substantial improvement when N20 slaved to my Merging +clock. So contrary to what Aurender manual says, a direct user experience always carries more weight in my opinion. As I said earlier, in my system adding a master clock was quite a revelation thus prompting me to bring in N30SA / W20SE for audition. For many out there, N20 should suffice. For me, I want to see how far I can push digital by upgrading the streamer and even a better clock down the road (yes, merging makes clocks at 3 performance tiers).
I hope you view this conversation as another tool to further enhance the performance of your N20. Having said that, at this point in your journey where you’re still figuring out DAC’s, streamers; you needn’t worry about adding the Master Clock or additional cost associated with it. To answer your earlier question about “in terms of the degree of sonic improvement per dollar spent”, IME a better DAC, Streamer or even Master Clock yields much higher returns on your investment over a fancy Valhalla 2 USB cable. Of course, your rest of the system should be appropriately balanced to take advantage of ultra high performance of upstream components. Cheers!