As others mentioned, particularly in your situation the first thing I’d do is try a filter before your Lumin. This SmoothLAN filter has been getting pretty rave reviews on another thread here, and at $254 with a trial period I’d consider this an absolute no brainer to try.
https://stackaudio.co.uk/product/smoothlan-network-filter/
After that and if still looking for further improvements I’d try a Lampizator DAC although there are many other outstanding choices at your budget from Bricasti, Weiss, T+A, Meitner, etc. that would all likely provide a significant and very meaningful upgrade to the DAC in your Lumin. Hope this helps, and best of luck.