If your primary wireless router can talk to you W306AV over the HomePlug AV, it sounds like you're doing it right -- set up your W306AV with the same SSID, Password, and wireless mode, and you'll have what's called a "roaming network". If you don't have connectivity between the two, I suggest buying yourself a 306AV or equivalent (I have three other brands of HomePlug AV / 200 Mbps equipment, and they all communicate fine), and hooking it up to a LAN port on your primary wireless router.
If you really want to extend your current WiFi network, you need another product. But if you're getting over 100 Mbps over your power lines, I'd recommend just staying with the W306AV and doing "roaming". I now have "roaming" wireless access in my garage (and a security camera to connect to it), which otherwise would have been a royal pain.