While I second your thoughts on Bluesound, a few remarks:
- The Aries Mini is currently in process of becoming RoonReady (beta firmware with Roon support is already available)
- IMO, a Pi with Digi+ Pro hat sounds quite a bit better over SPDIF than Sonos does. The same goes for the top-of-the-crop in DAC hats – try comparing with an Allo Boss, for example.
- DietPi supports 192kHz over HDMI (although limited to 16-bit, I believe) and up to 384kHz for most DAC HATs;
- For USB DACs, the Pi supports all of the rates that the DAC can handle, up to 768kHz
- Meridian are getting woefully behind the curve in networked audio with the 96kHz limitation still present on their networked options. Maybe the upcoming 218 will improve on this.