You need to install the usbip server on the computer the real USB device is connected to. If that is your Wifi router, you need to be root on the router, and you need to be able to install custom software (or have installed a firmware which provides the usual Linux software as packages, e.g. OpenWRT, DD-WRT etc. This is probably easier then messing with a rooted proprietary firmware.).
On the laptop, you need to install the usbip client. The Onkyo will than show up as USB device on the laptop, so it doesn't matter how you manage audio devices.
More detailed installation instructions shouldn't be hard to find with a bit of googling. If you get stuck, edit the question and describe what you've done and where you got stuck.
Another option is to install Pulseaudio on the Wifi-Router (again, that needs open firmware), configure it to use the Onkyo, and also configure one of the various Pulseaudio ways for remote audio access (RTP, RAOP, whatever; see Pulseaudio modules. In a similar way, configure Pulseaudio on your laptop. Then you'll have an additional "remote" sink on your Laptop, which you can use like a local sink.