airprt extrm 7.9.1, express 7.8.1 via wifi to hifi

7.8.1 firmware on the express is known problematic.

I recommend you reset the Express and set it up from the Catalina computer.. if it then works check the ElCapo machine.. if it fails on ElCapo you merely swapped which computer has control.

One of the key factors in the setup is IP address.. if set by DHCP should be changed to static on both the Extreme and the Express. Catalina is worse than ever with forgetting device IP around the network.

And if that does not work take the firmware back to 7.6.8 which works a lot better in the opinion of just about everyone who has issues.

is there a substitute for my present wifi system (I have a modem from my suppler with a built in router), that would also feed the amplifier as at present?

Basically no.. the Express is pretty much unique.. there are better ways to run it..

Ethernet directly from the main router with wireless off.. far better than setup to extend wireless on the Extreme.

If you are stuck with wireless though and the Extreme is still working OK that is probably the best you can do.

Post a few screenshots and we can give some advice on the setup.

From another Ray.. to Ray.

The StingRay

LaPastenague.

LOL.. Other Ray!!

Don't you just hate "everybody loves.. R.. !!"

Downgrade firmware in the Express.. you can do this from the computer that still recognises it with elcapo.

Hold down the option key while you click the current firmware number.

Select 7.6.8 and upgrade to earlier firmware.. upgrade because it works.. unlike the latest one which is downgrade i.e. doesn't work.