buzz456 wrote:The only problem is this appears to be for Brand x not Railworks.

It seemed to me the OP knows his way around sounds. Swapping one sample for another is not difficult, setting up a complete sound stage probably is.
I'll do a quick check of the GP9 sound setup, I already checked the railsim.com file's contents. It has sound samples for every notch, both going up and down.
I think the sound samples are interchangeable, if not the same. Perhaps Anthony Woods authored the Railworks sounds using his MSTS sounds?
The Railworks sound stage also has unique samples for the prime mover going through the notches, both up- and downwards, so these can be swapped quite easily.
The other samples concern air hisses, spits and blasts, ventilator and dynamic brake sounds, etc. The samples being ordinary .wav files, can be played back using any audio player/editor, unlike the mutilated .dav samples Railworks uses, these need to be converted to .wav first in order to be listened to
Most of the Railworks samples could be swapped for MSTS samples. Perhaps the mix of volumes needs to be adjusted a little to achieve a convincing sound stage.
Overall, given the number of samples the default Railworks GP9 uses, it is one of the better locomotives sound wise already. I doubt much can be achieved by changing it, but I'll leave the challenge and final judgement to the OP.