Sounds great on my Behringers.. you find a very clean and good sound sample for the engine,in game it's identical to the real one.
I hope that you will go for the rest of the gt3 field :)
Finally good sound for the GT-R, love the downshifts onboard - got no engine sound at low rpm however, like Sebastian. Otherwise spot on, keep it up. :)
If you'd like to install it manually, you can grab both the files in mods 'sfx' folder and place them in 'assettocorsa\content\cars\ks_nissan_gtr_gt3\sfx'
Perhaps while extracting the files they went to one of the parent directories