Hello Ian,
Let's see if we can make this work (it does work on my NAS, even though it is not connecting through myasustor.com, but is on a private domain).
First things first:
1. Make sure you have enabled the Web server (ADM, Services, Web Server, Enable Webserver (by default on port 80)). You do not have to enable personal websites, these are user specific websites.
2. Open your browser from a PC able to connect to the NAS and type
http://<local.ipaddress.ofyour.nas (ADM, Settings, Network, LAN, IPv4 address if you have a fixed IP address on the NAS)
3. It should open the website index.html located in /volume1/Web on your NAS. Because I have overwritten mine I don't know excatly how it should look, but it should give an Asustor message.
4. Enable SSH access to the NAS (ADM, Services, Terminal, Enable SSH (by default on port 22) and enable sftp service)
5. Download WinSCP (in case you already haven't) and start a new session to your local NAS ip address, use your admin credentials to connect.
6. You will now be able to browse your NAS like a regular drive
7. Copy the .php file to /volume1/Web
8. Open your browser and type
http://<local.ipaddress.ofyour.nas/<name of file>.php
It should now give you the PHP information, once this is working it should not be hard to get it working from the internet.
Please let me know how you go and which steps work and which don't.
Best regards,
Kapitein Haak.