Okay, I just re-read the specification, and the sampling rate is definitely a factor. It's not just twiddling a byte. At least it looks that way to me from my quick glance.

I think you're now into the realm of talking about SAMPLE RATE CONVERSION, which is a whole big can of worms unto itself. There are companies (high-end audio editing software) that actually have patented algorithms for sample rate conversion. It's not a simple thing to do correctly. You will lose some quality in the conversion, and you might want to avoid trying it, in favor of just going back to the original source material.