What to replace my Airport Express with?

I've just swapped out my Airport Extreme router (400Mbps max) for an xFi Gateway: 600Mbps max.

No Airport Extreme I discovered means no functioning Airport Express.

I used the Express not so much to extend wifi signal (though it likely helped) but as a way to add ceiling speakers in our kitchen to the wireless network to be able to play audio from iOS devices over these speakers. They are wired to a ±13 year old Onkyo AV receiver (without USB or Ethernet jacks, but with audio and HDMI out jacks) . I used the receiver's audio output jack and the audio jack on the Airport Express to make the connection.

Scoping out modern extenders, I see they only have ethernet jacks, perhaps all of an "IT OUT" variety: which sounds like they only work in one direction?

Will the following work to duplicate the functionality I had with Airport?

• Buy an extender with at least one ethernet port
• Using the requisite plug adapter, connect the extender's ethernet plug to either the receiver's audio jack or HDMI jack.

If not, do you have a suggestion on alternate path to achieving this?

Many thanks in advance for your guidance,

Peter L