One place, as far as I can see.
The question of interest would be if the Uni Box S3 really can linked with WiiM products, only, but not with other Linkplay based products. Honestly, I doubt it. Customers usually don't know if their device contains a Linkplay module, but they do know if they own a WiiM product. I suspect they didn't want to name too many competing brands in their manual.
As has been discussed in those other two threads everything seems to indicate that Pro-ject are using a somewhat older Linkplay module.