I've had issues with SXM and the Autonomic-manufactured Nuvo MPS4E for years.
One person I know reboots every evening, or once a week (on a timer), can't recall specifics.
Rebooting the MPS4E works for me, reliably. Changing the output to something other than SXM, and then choosing the SXM channel again is a quick fix, without needing to reboot.
This is one of the reasons I'm ditching the MPS4E, moving to Sonos.
I would call Autonomics (and not SnapAV). They recently split - old owner of Autonomics bought it back from Snap.
TB A+ Partner Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha