Without doubt the sweet spot is the Aurender N20. Other server/streamers maybe fractionally better but nothing will blow the N20 away. You'll need to spend at least twice the price to get any slight improvement.
It also has a master clock input.
My setup is N20, solid silver USB cable, Musetec 005 DAC optomised for USB.
Other DACs may prefer AES/EBU digital but you can't play native DSD.
DACs are starting to be sold now using the new ESS 9039 PRO chip. This will increase price/performance.