It wouldn't surprise me at all if FMod cooked the sound a bit to achieve a better impression with the paying customers.
For OpenAL I'd say that this being a free and open source library, no such antics are needed.
This reminds me of some DVDs from the early 2000's where often the DTS track also was postprocessed to make it sound superior to the Dolby Digital version - and it often worked, never mind that for people who had a bit of knowledge it was often unmissable that the sound had been compromised.