Compatibility WiFi 6 (802.11ax) mode

Hi there.

I recently upgraded my router to a Wifi 6 (no extender or mesh). 

I have

3 x older Play 1s (2 as surrounds)
1 x Soundbar
3 x One SLs

I have found that, using 2.4GHz wifi, the 3 One SLs (i.e. newer hardware) work just fine however the older hardware cannot be seen on the network

UNLESS I turn off Wifi 6 mode and go into a compatibility mode… Then everything is fine. 

As a workaround, my house is Cat 5 wired (and a couple of units are placed to enable connection directly to an ethernet port. I therefore connected the Playbar to try and create a hard wired configuration… It seemed that this didn’t work either, with an inability for anything to be seen / configured by the iOS app…

My questions are therefore:
1. Am I right to assume the Play 1’s and Playbar will not work with Wifi 6?
2. Because wireless router remained on whilst trying to config in wired mode, has this prevented a wired mode setup working?
3. What is the range of using SonosNet (i.e. wired mode) vs WiFi?
(and finally) 4. Would a Boost alleviate all my woes above and thus enable me to use WiFi 6 in my house?

Appreciate someone’s help on this. 

Thanks