Glad you got it sorted.
I downloaded it and looked a bit closer.
There is no sound folder in the pack at all.
The aircraft cfg says sound=herc (or Herc - makes no difference). So the instruction is to find a folder called sound.herc and use the info in the sound.cfg inside that. No sound.herc folder means no sound.
If you create a folder called sound, with nothing in it, and change the aircraft cfg to sound= ,you usually finish up with the default Cessna sounds. (BTW, I think this is where the [General Engine Data] bit comes into play - if you set it to engine type=1, you would probably get the default LearJet sound. I don't know what else it does.)
[GeneralEngineData]
//0=Piston, 1=Jet, 2=None, 3=Helo-Turbine, 4=Rocket, 5=Turboprop
engine_type =0
When the aircraft cfg says sound= ,any folder called sound will work, provided it has a config file and sound files in it. If the sound cfg says alias=anotherplane\sound then you need to have that other plane installed with a valid sound folder.
The Halifax [flightsim.xx] numbering goes from 0 - 14, so if you really wanted to, you could use 15 different soundsets, so long as each had its own folder (sound.aa , sound.01, sound.gj and so on) and each [flightsim.xx] section called its own sounds (sound=aa , sound=01, sound=gj and so on)
You can do the same thing with model= and *.air files .This would allow you to have several Lancaster and Halifax types in one aircraft folder - some Lancs had radials, and some Halifaxes had Merlins. In the old days when hard drives were very small, this saved a lot of disk storage space, but it hardly matters these days.
Cheers
MikeW