lhemingw wrote:
... I know that Apple is not doing airport utility anymore.
Since all my networks are using Apple equipment I'm hesitant to say anything at all, but that statement is not true.
Follow Tesserax's instructions but I believe you will need to "hard reset" the Express according to How to reset your AirPort base station - Apple Support. You will then use AirPort Utility configure the Express to join the network in client mode. To do that you will need your Mac to join the temporary wireless network it creates for the sole purpose of configuring it. When it finishes and the Express restarts, that temporary network will cease to exist.
It may be necessary to connect the Express to your Netgear router with an Ethernet cable. Again, I'm hesitant to say that only because all my network routers, access points etc are Apple, and am not in position to confirm an Express can join another wireless network in client mode. It can almost certainly be added to a wired network though, and should appear as an available device for AirPlay streaming.
On that subject, have you given consideration to having the Express serve as your primary router? It can do many things including that, but of course you will want it to be physically near your HK sound sticks. You will need a long audio cable (or optical cable — the Express's audio output is a combination analog / optical output port) or an equally long Ethernet cable going to the ISP's gateway (modem) if you want the Express near the sound sticks.
If something goes wrong during configuration and the Express's LED does not go from flashing amber to its normal happy green, you need to start at the beginning: "hard reset", join its temporary network (named "Apple Network <...>"), configure with AirPort Utility... etc.