The fssound.dll goes in the modules folder.then copy and paste this in the FS9cfg file.
[OLDMODULES]  
FSSound.dll=1

if you dont know where the FS9.cfg file is see the post FS9.cfg.
this is the only way to get that panel to work and not get the error message.i dont know what you said you deleated but i dont think you should have done that.but maybe it wasnt something important.but if your going to use addon panels with sound gauges.then yes you need all these files and information in its proper place.and the FS9.cfg and the fssound.dll. files are hid from view unless you have show hidden files checked in your windows opperating system.hope this helps you out.if you have any more problems with it theres many around here that know a thing or two on these matters and will help you out includeing myself.

You can paste it at the bottom of the FS9cfg file that would be fine.and save it.but it will load the fssound.dll into the sim and stop the error message.if you have the fssound.dll in the modules folder in the sim files and the other pasted in the FS9cfg file.thats all there is to it.and it should all work and alls well again.