I've found that AOTS uses XAudio2_7.dll because XAPOFX library needs an older method named SetEffectChain. (It is the only old method.)
I've tried to add in the AOTS folder all x64 DLL available of CAT files of the _CommonRedist\directx folder, without success (still no sound). (I have not overwriten already-existing DLL in AOTS folder.)
I've tried to install Visual Studio x64 packages (as admin) but without success. They seems to be useless on Windows 10. So I've uninstalled it.
Finally and resigned, I've installed DirectX dependencies (as admin) and sound works. That is not the solution, I know, but it shows that DirectX dependencies are needed to have sound (on Windows 10, I don't know for older Windows versions). But how configure it manually?
I always talk about XAPOFX but I've not explained why. (I'm talking about when you have NOT installed DirectX dependencies, of course!) In fact, AOTS audio needs XAPOFX library. XAPOFX1_5.dll is not included in the AOTS folder, unlike XAudio2_7.dll. If you don't have it, AOTS doesn't launch at all. But if you try to add XAPOFX1_5.dll (for x64) manually in AOTS folder, AOTS can be launched but you don't have sound. I haven't found why.
If someone knows what does exactly the DirectX installer, or XAPOFX library or a Windows installer, I'm really interested. I was thinking that DXSETUP (June 2010, provided with AOTS) only add DLLs files in Windows System32 folder. Maybe it is interresting to audit system changes during DirectX installation, but I don't know how do it.
Like Rustyy117, anyway I hope this helps someone else.