Is it possible to downgrade the Multy X firmware

Update: I confirmed my issue is not related to Multy router and I no longer have a need to test downgraded firmware. I tested this setup with my Netgear nighthawk router with the same problem behavior. Im off to figure out if it's Pandora or Sony.  Leaving the rest here for sake of others.

Issue is the Pandora audio cast is choppy or does not stream music at all and disconnects from the cast session. 

My issue occurs 100% of the time when all of these are combined:
1. with Pandora only (Spotify, Amazon, Deezer, Google Play music, all work fine)
2. using a) current version of the Pandora Mobile App to cast  Or b) asking the Google Home to start playing music 
3. the Google Chromecast Speaker Group being used to includes (2) or more of the Sony HG1 speakers.  

I have (3) Sony HG1, (1) Google Home, (1) Polk Mini MagniFi.   For the past 2+ years, I've had no issues playing Pandora to the speaker groups including all 5 speakers at once, individually, or grouped in pairs, etc, as they are throughout my house.   

I have recently confirmed my issue IS directly related to Pandora's latest versions of its Mobile app because using a prior version of the Mobile app does not have the casting issue. However, that doesnt explain the issue occuring with condition #2B above, when starting the music stream from the Google Home, because it is not using the mobile app at all.