By chance, I came across an article about the Sena 60S where the author mentions an alternate method for connecting disparate intercom brands by setting up a WhatsApp group call. Yes, this will require a solid mobile phone signal (so useless in north Wales) but if all else fails, surely worth a try ? Andy
I know Jetski safety crews have been using this method with just cardos to gain range, makes sense it will be a workaround for the sena cardo issue, which is just dumb in this day and age.
There's also a dedicated (Sena developed) app called Wave which claims to perform the same function, ie, create the connection using users' mobile data, but it's not reviewed very well as far as I can see.
Purely commercial, both want to dominate the market, neither want to compromise or share. Memories of Sony (Betamax) vs JVC (VHS) back in the middle 1970's. Andy