As long as you don't want Atmos, DTS-X, or Auro 3D, JRiver all by itself can decode all the legacy codecs, and with a multi channel DAC like the Octo Dac 8, you can indeed replace an AV receiver for all digital files and anything that streams over a PC. You can't, however, get the contents of a copy protected silver disk to play via the PC without first cracking and ripping it.
I currently use a $260 fanless Mele Quieter 3 to create a 5.1 system with no receiver using an OCTO Dac 8 Pro as my multichannel dac.