If you have an 818v3 it really is at its best in combination with Roon I am afraid. An 218 will also only stream using Roon. You can use the USB input of a 818v3 but others have reported here its superior using it ID41 card.

You could buy a 210 and use it as an UPnP streamer, and upgrade the PSU? If you are going to use the digital output of another streamer to the 818v3 and then to DSP speakers I doubt the 818v3 can add its value.

Main: DSP8000SE< 218 < Farad Super3 TMCB < PS Audio P10. Room correction: Focus Fidelity.
Second: Fostex Fe206NV2 < Audio innovations 500 valve amp < Wiim Pro +
Study: DSP33 < Reviver < MS200
Server: ROCK + Tidal on NUC, fiber on 2x cisco 2960, HD-Plex LPS.
Gone: DSP7200SEu, DSW, DSP5500mkI & DSP5000mkI, 508.20, 210