All my other sounds work fine thru FSX.
This doesn't mean much: GSX requires OpenAL to be working properly. If your sound driver doesn't support OpenAL, or doesn't support it properly, you'll hear sounds in all applications, except those requiring OpenAL, and GSX is one of them.
Those I did not install were all internet security-related so should not effect internal functioning of any software. I have UAC off and I operate FSX with internet and virus disconnected so should have no interaction from these. Other than that...?
Don't assume that something that is named in some way (like "security hotfix against intrusion") doesn't have any other repercussion on the entire system if not installed. Almost constantly, Microsoft includes updated Visual C++ runtime .DLLs together with their Hotfixes, and they impact basically everything.
So, try again and let Windows update everything, even optional things, optional hotfixes and drivers.