Slightly different question - assuming I’m not going to connect the SP2000T what equipment do you need to get the best from the ERA 300 speaker ? If you input 24 bit 92 KHz it knocked it back down to 49 KHz ? Not that I suppose I would hear the difference.
Personally speaking, I would not choose to use the Era-300 line-in and just use the local internet connection (wireless, or perhaps wired using the Sonos network adapter) and stream Amazon Music HD/UltraHD from the Sonos built-in services instead, which will play Atmos and stereo audio tracks up-to 24-bit/48kHz …and there’s plenty of tracks to choose from.