Given that I'm not using the stereo feature I need only worry for the moment, in my experimentations, with the .prs not having an "i" or an "x" in its name.
After listening to the various samples with Media Player, I made these two changes:
In motor.Sakae.prs, for the inside samples I use the exterior samples beginning with "x_".
In motor.PrattWhitney_R-2800_Series.prs, for the exterior samples (not distant) I use the interior samples which do not have the preceding "x_".
For the Zero and the Hellcat this makes for a small improvement, less so for the Hellcat. Note that in both cases the same samples are used for the inside and near exterior.
The sound continues to suffer too much of a white noise contribution. Before this experimental change the exterior Hellcat motor sound was probably 75-80% white noise; now it's about half 'n half--and of a low volume that remains constant until the transition to the distant sound kicks in (whereupon it actually increases in volume a tad at that crossover due to the overlap of the samples.).
On balance, many exterior motor sounds are a weak, thin, reedy, hiss that's as much engineless glider as a supposed war beast.
While testing the Hellcat, the interior gunfire is almost inaudible, while outside it's louder than the engine. From near the plane and fairly far away, the gun volume beats the engine. Only around the transition between near and distant motor sound, where the two samples are at max overlap and hence where the engine sound is actually loudest, are the gun sounds a bit quieter than the engine.
Back to the interior Hellcat. While firing the guns, the near silence from them allows an odd sound to faintly come through which seems to me to be the airframe stress sound being activated periodically. It's not very distinct, largely due to the dominant white noise, but its coming and going does give a fair hint to its presence.
Is it possible for the shaking of gunfire to cause any momentary G-load spike which could trigger the stress sound? If not, then this would seem to be another clue to the generation of unnecessary/unwanted sounds. Like the dominating white noise I am suffering. Like the rain sound in good weather just because I had raised the altitude zone within which it could be heard.
Puzzling aspects abound...