I just bought a RPI4 with a DigiOne Signature. I am using it with MoodeAudio and a BubbleUPnP android app as a controller. So far I am underwhelmed by the sound. It sounds a bit harsh at the top end. I have Tidal and Qobuz subscriptions. I also bought the Shanti linear power supply.
I have an RPI4 with the DigiOne (not Signature) running Moode and it is a significant upgrade from my Sonos Connect. I am not sure how BubbleUPnP might be affecting or manipulating the chain of sound, but suggest you try removing it from the chain and use the moode interface directly by going to moode.local on your browser. Also curious what DAC you are using and how you are connecting from the DigiOne to the DAC.