There is no fixing it, hence the documentation. An Amp in surround mode loses it's Line-In and sub out due to the special one way ad-hoc 5 Ghz network setup for low lag connection to the surrounds.
So then sonos doesn't support subwoofers for surround sound?
So then sonos doesn't support subwoofers for surround sound?
Not at all. They support Sonos Subs, or a 3rd party sub if the Amp is used to power the front speakers in a surround setup.
So then sonos doesn't support subwoofers for surround sound?
Yes, when the Sonos Amp is managing the front TV HT channels, then a 3rd party ‘active’ Sub can be used, just not when it’s a slave device, handling the rear channels. Oh and of course with either type of setup, the user can use a single Sonos Sub Mini, or up-to two Sonos Subs. (Note: when using two Sonos Subs in the same HT ‘room’, one must be a Gen3 Sub).