Audirvana has the best sound I found, and that's on a very modest office system that differences can be heard compared to Jriver.
Audirvana is vey slow to scan network drives for changes, pity the engine can't be used with another server program.
Gave up on Roon now 2 years ago, not supporting bully tactics from software authors. Fixing up metadata and sending the data to Roon where it claims to be metadata master was the last straw. Roon didn't sound all that great and is fickle about network.
Pity the OP doesn't have the X1 any more. Minimserver is a bullet proof server and it's the best server I hear for the U1.