OK, I completely uninstalled FF7 Steam and PC, then I manually deleted any folder remains. I then ran the reg fixer provided in the FAQ section, as well as CC. My computer is completely FF7 free (bar the 7H iro folder, which I kept). Then I installed the Steam version to C:\Steam Library, but not the '98 version
I disabled my antivirus (the threat was one of dlpb's .dll files which I've restored), then I ran the GC as administrator, making sure to select a sound source in the ff7 config. I received an error message after imstallation that the software ahdn't installed correctly, and gave me the option to run under recommended settings, which I followed (the same error occured after the initial installation too, I'd just forgotten about it).
Afterwards, I followed the exact steps for 7H setup as I did the first time round for the same result. No mods have loaded, and no sound. VGMStream selected. I haven't installed the '98 version yet, but I suspect the same result as yesterday; working mods with the crappy audio. I'll report back