IR control of devices was always meant to be a customized procedure. Audio and video manufactures try to make it universal by including codes for other devices for their remotes. But the codes are almost always inadequate for anything but the simplest system. Very few people are ever successful in using a TV or a receiver remote to control all the necessary functions.
If you are going to support IR/RF (RF for all those people who do not have direct line of site to their equipment) commands then, as Brian says, you need to supply codes a full range of devices. Remote companies like URC and Harmony/Logitec do that, but it is a signficant amount of work. Even within the same company, different models of the their TVs use different IR codes.
Programming a remote control can be quite complicated if you have than one or two devices. Ideally you also need to know the state of each device, especially if it does not have unique codes for some functions, e.g. like most DVR boxes.
Harmony will automatically produce a set of code that runs in their remote, assuming they have all the IR codes. It works for simple systems but for more complicated systems it is often only partially successful. At that point, the user has to learn to program their remote through the Harmony software, which takes some effort.
Let me give just one example where things get complicated. Say you want to use Amazon Prime or Netflix on your TV or on your Blue Ray player. Some devices have a single IR command to pull up that app. Most do not. So, you need to do some macro - like Menu, Down Arrow, Down Arrow, Enter, Left Arrow, Left Arrow, Left Arrow, Up Arrow, Up Arrow, Enter. That gets complicated pretty quickly.
And, unfortunately, there are still TOAD devices out that - that is, toggle only devices with no direct on/off code, just toggles. That is where the state of the device becomes important.
Other companies like URC, Control 4, Creston have their own programming languages and interfaces. These allow very customized systems, but can also be complicated to program. Most users will not be able to handle that programming.
I have a small side business programming remotes. I always ask people if they want to learn how to do it so they can make changes. Almost nobody ever wants to do that. For many, even doing Harmony is somewhat difficult. Now, many MC users are relatively sophisticated so could handle some simple Harmony like setup. But a large number of your users would probably not be able to do it.
Also people with real audio systems are probably not going things like a Z Wave power strip. They already had hundreds if not thousand invested in a power condition which often is not controlled by IR or RF. Some power strips will turn on with an IR code, but again, you need to somehow assemble those codes.
I suggest you find someone who does home automation with remotes on a regular basis. Other than being protective of their business, my guess is they will tell you it is often much more complicated than you may think except for a very simple system. You might be able to do something for very simple systems, but to even do that you need the IR codes for the devices, which, as I said, are a lot of work to come up with.
You might want to go to RemoteCentral and browse the Customer Installer board to see what troubles professionals run into. Now, they deal with complicated systems, but you will start to see the issues.
Personally, I would not suggest you try to compete with the learning remote companies and custom installers. That leaves the installation with a TV, BR player, receiver and not much else. You might be able to do something there. But, honestly, Harmony is probably a better solution for those setups.
By the way, CEC can be very problematic. It does not always work across different manufacturers and sometimes not even within the same manufacturer. I would be careful about using it as a universal solution. Again, you can do some reading on RemoteCentral about it. Those guys are down on most new things, but they do have examples when it has proved very problematic for them.