Ok, so you spent money to get a better experience with the Original Rift. How is that different than spending money to improve the Rift S experience? It's only a £16 upgrade which is much cheaper than a sensor was for the original Rift.
The thing is, you might not even need to do the mod, you might find the audio perfectly fine. It seems to depend a lot on the how the headset fits the user's head. The lower you can wear the strap, the closer to your ears the speakers are and the better the audio. The positional queues are much better with the Rift S than the Rift. But the Rift S is lacking in the bass department.
Just other info, the tracking on the Rift S is about as good as a three sensor setup on the Rift. Not as good as a four sensor setup. (I had a 4 sensor setup)