Start by looking at the documentation for what your speakers accept as an input.
Then look at what your interface is able to output.
I don’t have the Klipsch speakers, nor do I currently use consumer-grade monitoring.
Having said that though my understanding is that usually when you see a speaker with a ‘speaker plug’ that receives ‘speaker wire’ it means they are un-powered and receive an amplified signal from somewhere. If it’s a consumer surround package it’s usually a receiver / entertainment center system that amplifies the signal.
The average computer interface we use for DAWs isn’t amplifying signals to speaker level, it amplifies to (“professional”) line level.
So my assumption would be that it’s not as easy as just swapping cables and connecting straight into your interface. I would expect you would either need to output ‘consumer level’ to a receiver and have that amplify to speakers, or have a receiver that accepts line level, or send to a receiver using digital.
If you send digital you’ll need to send 6 channels for 5.1 and you’d have to make sure that the receiver can accept whatever format you’re sending. I think your interface can send ADAT signals over optical and that’s a maximum of 8 channels at 48kHz so that’s what your receiver would need to accept. Some devices send surround over S/PDIF but then it’s already encoded and you’d need to encode which I recommend you don’t try to do.
Last option for digital is HDMI maybe? Your interface doesn’t have it, but your computer might (?). You’d have to again check that all devices can accept that, and then you’d have to select that audio device (computer) as the output in Cubase/Nuendo, which could be annoying because I bet you wouldn’t be using ASIO drivers for it.