Best Way To Connect My KEF LSX

Hello All. Got my Nucleus up and running thanks to some kind folk here. Now, I’m wondering what is the best way to get best sound.

I have the new KEF LSX wired to each other, then to my router. They show in Roon as endpoint and sound great. BUT I have a Meridien Explorer 2 DAC that unfolds MQA and connects to my iMac via USB.

Should I use it and how should I connect it ? I’m hoping not to use the spare USB port on my Nucleus as I’m going to try to connect my Audio Engine speakers in my bedroom to that port via a connector they sell.

Before I got the Nucleus and my Roon Core was on my iMac I had them from the LSX Aux out to the DAC to the Usb on my iMac but it didn’t sound as good to me. But not sure perhaps I did it wrong.

Any suggestions/advice is appreciated. Thanks!