Hi. A few niggles you guys may help with.. If airport express is used to extend network, can it still be used for airplay?

If airport express is used to extend network, can it still be used for airplay?

Yes

I have both 1st and second gen units, which one would be best wired via ethernet to router

The new device will deliver dual band wireless if it is connected via Ethernet. But, the new Express will not extend both bands if you use the old Express connected to the Ethernet connection as your "main" router.

ive been using a TP-Link plug in wi fi extender so would this new set up negate this

Yes

and be better or worse?

Impossible to know until you try it out in your own environment....unless someone else here is able to predict the future. 😉

Yes....that way you can take advantage of the dual band capability of the "new" Express in the area where that device is located.

If you make the "new" Express, the extender it will only extend the single band that it receives from the "old" Express....so you lose the dual band capability of the "new" Express if it is installed as the extender.

As far as performance is concerned.......a good wireless setup will almost always beat a powerline setup because there is so much loss in the powerlines. But, as you know, wireless can have issues as well. You just never know until you try.