Revnice-Do not do what you just stated!
Looking at the Onkyo manual it appears that to use the Line Out of the receiver, your Emotiva amp would need a separate volume control. Like Sfar said you should be cautious of hooking up amps to Line Out outputs as they typically are not attenuated. Sadly I think your receiver will not allow you to control a separate amp without the amp having a volume control.
You can try hooking your amp up to the Line Out with volume all the way down but you may end up damaging the amp or speakers.
Looking at the Onkyo manual it appears that to use the Line Out of the receiver, your Emotiva amp would need a separate volume control. Like Sfar said you should be cautious of hooking up amps to Line Out outputs as they typically are not attenuated. Sadly I think your receiver will not allow you to control a separate amp without the amp having a volume control.
You can try hooking your amp up to the Line Out with volume all the way down but you may end up damaging the amp or speakers.