Music server questions

sounds like an Innuos product for you

Innuos  would also be my recommendation.

This is the best option I can think of for your budget:

https://www.cambridgeaudio.com/en/products/cx/cxn-v2

Another route could be putting something like the Mutec MC-3+USB between your laptop and DAC. That particular unit reclocks, has galvanic isolation, and has SPDIF coax (though not optical) outputs.

I should mention my system
Bryston power
Audio Note M3 line pre
Audio Note 3.1 Dac.
Various speakers. 

I really like my Dac and have no interest in replacing it so servers with a Dac are not required. I really the convenience that a lap top provides  but feel I may be missing something with the sound quality a good server can bring. 
Used market is fine to. 

Salk Steamer.  Let Jim know you need optical. 1695.  It’s fantastic for the money.  Has a hard drive, can be configured to use a keyboard and monitor I believe.  Roon core installed.  I would give Jim a call and talk with him at a minimum.