Hi Steve,

I have now removed the 218 and connected the Sonos direct to the master coax connection. Still does not sound good.
You asked if there is any output form the tweeters, I am not convinced that there is. The Issue could still be the Sonos box so I need to try something else. If it were a speaker hardware problem why would that be evident on both?

Thanks

DSP5200SL, 218, with Sonos. Rest of home Loxone multi room audio with Monitor Audio speakers