Use the NVG589 with another router and have DHCP enabled on both?

Summary:

Scenario 2 seems both standard and optimal but doesn't work with the NVG. (See below.) Scenario 3 also seems standard but suboptimal. Scenario 1 worked for a while but we suspected some issues. What do we need to consider before switching from Scenario 3 back to 1? Any help is greatly appreciated!

General setup:

We’re on Uverse internet 45 mbps and voice service. An ATT NVG589 modem/router and a TP-Link Archer C9 router sit right next to each other on a bookshelf in the middle of a 50-yr old ranch house. Out of the back of the router, we run two cables to ethernet ports in other parts of the house and we also connect to a Sonos bridge and a WDMyCloud device (and obviously the routers are connected to each other.)

Details to consider:

1. IP Passthrough mode on the NVG5x9 (with current firmware) interferes with Uverse voice (personal experience confirmed by the ATT forum).
2. Sonos is incompatible with the NVG device (personal experience confirmed by the Sonos website.)
3. The MyCloud is incompatible with the Archer if it’s configured as an access point (personal experience confirmed by the WD forum.)
4. Don’t think this matters but just in case: We have a TL-WA901ND set up as an access point in a sunroom addition that is around a brick wall from the main router.

Scenario 1 (from Nov 2015 until a week a go): Connect from LAN on the NVG to WAN on the Archer. Turn off the wireless on the NVG. There are two subnets but all clients (wired and wireless) are run through the subnet that the Archer manages. Both routers have DCHP enabled but only the Archer functionally assigns IP addresses within the network. Are there still potential conflicts as clients talk to the internet and the internet talks back?  I don’t think the NVG changed its DCHP-assigned IP of the Archer in the 7 months we were set up this way. Sonos and MyCloud are verifiably happy behind a fully functioning Archer.

Scenario 2 ( with IP Passthrough enabled for 24 hours)

Set up like scenario 1 but turn on IP Passthrough on the NVG. Until we discovered we couldn’t get incoming mobile LTE calls, this seemed optimal.

Scenario 3 (since disabling IP Passthrough): Connect from LAN on the NVG to LAN on the Archer. Configure the Archer as an access point. (Disable its DHCP and set a static IP address outside the DHCP range on the NVG.) Turn off the wireless on the NVG. There is only one subnet. The NVG talks to the internet and also assigns all IP addresses on the LAN side. The Archer provides its dual-band wireless. Although we don’t have enough data yet, the MyCloud seems okay as long as it’s connected to the NVG. We’re less sure about whether the Sonos can manage reliably one device away from the NVG on the same subnet. We have obviously lost the Archer’s excellent router functionality.

Go back to Scenario 1? Badger ATT for the 5268ac gateway that allows a fully functioning router behind it? 

Thank you!