In order to have a web interface you need to have a web server on the PC or HTPC that controls your AV system. A web server is not something that a non-professional would even want to be responsible for, and is also something that may violate your ISP's terms of service.
The proper way to accomplish Internet remote control is through a client/server system, where only the specific software client can obtain port access based upon a successful encrypted authentication process. Any other type of connection attempt is simply dropped as if the port had been firewalled all along.
If you expose your system to the Internet using anything less than this, you may be in for a very enlightening experience. A hacker defacing a web page is not uncommon and obviously a nuisance, but a hacker that can max your AV systems volume out for hours while your away is a completely different matter.

If all you need to do is provide control from another PC on your home network, running a tiny secure client software interface is certainly no harder than opening your web browser and it can provide much more elaborate control than any web interface could. The network remote version of our HD Radio receiver control system is a pretty good example. It would be quite impossible to provide the level of security required to legally transmit radio station audio over the internet using a web control interface, and those that try doing this from an insecure web interfaced system would likely find themselves in court being sued by the RIAA for an unlicensed public broadcast. The client server system we employ provides secure place shifting such as this over the internet without the risk of unauthorized access to the audio stream.