adding a wireless router to a wireless hub

I have no idea what a sound bridge is, but if you're having signal issues, then the best solution is to add a second access point. (I assume by wireless hub you mean an AP). If you disable DHCP on your wireless router and connect it to your network using one of the LAN ports, then it can function as an AP as well. However, this requires a physical connection to the network somewhere near you for the router to plug in to. There are a few wireless repeater products out there that might work, but I have zero experience with them. Google is probably your best friend for info on them.