Hello, I would like to ask for some help.

I just upgraded my Archer C2600 with Deco X20. 

Although I would have liked to disconnect my Archer C2600 entirely, I happen to have two devices that I want to have connected to the network via ethernet and because a Deco X20 only comes with two Gigabit ports, what I had to do was connect the WAN port of Archer C2600 into one of the Gigabit ports of my main Deco X20 after using the other Gigabit port on the main Deco X20 to hook it up to my modem. I couldn't use the Gigabit ports of my secondary or tertiary Deco X20 because theose other Deco X20s are placed on different floors of my house while the main deco is on the second floor together with my VOIP adaptor and computer.

So, then I connected the two devices that I want connected via ethernet (a VOIP adaptor and a computer) to Archer C2600 via Lan ports. I also have a USB external HDD connected to Archer C2600.

I disabled both 2.4HGz and 5GHz wireless radios (since I now have the wifi from Deco X20) and I also disabled DHCP server on Archer C2600 and enabled USB access.

I have two questions:

1. Is what I described above a correct configuration? On the iPhone Deco app, I only see Archer_C2600 as one of the clients, but I don't see the VOIP adaptor or the computer separately, which are behind Archer C2600, listed as clients themselves. I thought my configuration would make Archer C2600 "transparent".

Where are my VOIP adaptor and computer getting the IP addresses from, if Deco is not "seeing" those devices, but only seeing Archer C2600 as a client (which, as I said, has DHCP server disabled)? I was looking for a setting to set Archer C2600 to bridge mode, but I couldn't find it in the web interface.

Can someone tell me if I set things up correctly, with Archer C2600 working as a bridge, or if not, can someone help me with it?

2. Somewhat related to the above question. The way I have configured it now, things seem to almost work, including that the VOIP adaptor and computer are both connected to the internet. However, I am having trouble accessing the USB HDD with my devices on the network that are connected wirelessly to Deco X20 directly. 

I can access the USB HDD as a SMB media server and also as a FTP server from my computer, so the USB HDD is definitely connected to the router and the basic settings are apparently correct. 

However, my iPhone, for example, can't seem to connect to the USB HDD. I am using an iPhone app that supports SMB and FTP, and I am sure I entered the correct IP address for the USB HDD. 

Why am I unable to access the USB HDD from my iPhone, even though I can access it from my computer? Is it because I didn't correctly configure Archer C2600 as "transparent" or as a bridge? But if I make Archer C2600 transparent, doesn't that mean that I won't be able to access the USB HDD from any device that's connected to Deco X20 wirelessly, since I assume Deco X20 does not come with a USB sharing protocol (Deco X20 does not come with a USB port).

I am pretty sure this should be doable, but I am stuck here.

I would really appreciate if someone can help me with this.

Thank you so much for reading.