For Commercial Use:
We have been using Open-Mesh access points at my work (specifically the OM5p-AC) and I love 'em. They connect to each other wirelessly, but I don't think they will connect to your existing wireless network wirelessly. I recommend that you buy two. Hardwire one to the router. The second one will connect wirelessly to the first one and act as an access point. Turn off the wireless radio on your router.
- Pros: Seamless wireless network with high availability
- Cons: Expensive
Some people might not like that you can only manage these access points through cloudtrax.com. There is no local management interface. I thought I wouldn't like this setup until I tried it, but I was converted when I realized that all I had to do to set up a new access point was plug it in and enter the MAC address on the website. They do support OpenWRT if you really want to manage them yourself.
For Personal Use:
What you are looking for is called a repeater or range extender. I have tried the Netgear N300 and it works fine. Plug it in and forget about it. It has an Ethernet port so you can wirelessly bridge one wired Ethernet client. If you need to bridge more than one wired client, the TP-Link AC1900 has four Ethernet ports.
According to page 87 of the user manual, you can put the AC3200 in Repeater Mode. I have tried re-purposing routers as repeaters and decided I didn't like it because they turn back into routers if they get reset for some reason (it's happened a couple times due to power surges). If that happens, you get a network with two routers, and then bad things happen (DHCP conflicts). Hardware designed for use as a repeater is simpler and more reliable.