Christiaan, are you saying that the port forwarding rules for VNC and file sharing are preconfigured on the router?
Port Forwarding is pre-configured for Roon, so that works out of the box from your home network, but for regular network access, such as file transfer from another computer, a new rule needs to be set.
To avoid creating a new port forward rule, you could connect a computer to one of the Extreme Router's LAN ports for the full 1Gb transfer speed. Or temporarily connect the Extreme directly to your home network.
If you are willing to dive into the Router settings, you can configure port forwarding, which is a bit more elaborate. We've put writing a manual for that on the to-do list (Still to do...). The Taiko Router does not work differently from any other router in that regard.
Preliminary information - How to set up Port Forwarding via VNC and how to configure File Sharing
Please note that we cannot provide support for non-standard procedures such as this one. The below information is provided as is. If issues arise, please be aware there’s always the option to return the Router to factory settings.
VNC
1 - On the Taiko Router to go Network-> Traffic Rules -> click on Add at the bottom
Click save; then click Save and Apply
2 - Go to Network-> Firewall -> Port Forwards-> click add
click save; click Save & Apply
3 - Go to your computer on your main router (wifi or wired) and open VNC.
Create a new connection or edit an existing one.
The IP address is the Taiko Router's IP address on your main router. In my case it was 192.168.1.180. This is not the Taiko Router IP default gateway of 192.168.100.1.
You should now be able to VNC to the Extreme using your main network.
File Sharing
1 - On the Taiko Router to go Network-> Traffic Rules -> click on Add at the bottom
Click save; then click Save and Apply
2 - Go to Network-> Firewall -> Port Forwards-> click add
Click save; then click Save and Apply
On a windows computer you should now to be able to into file explorer and Map A Network Drive.
In "Folder" type in \\192.168.1.180\music where "192.168.1.180" is your Taiko Router IP address (same as with VNC)
The username and password are the same credentials as VNC as well.