I really like your idea to have the Attenuation field represented in true dB. My last SoundFont project was to convert an SFZ instrument, and I had to run all of the attenuation values through a calculator. This feature will save me a lot of time in the future.
Also, I can verify that velocity-to-attenuation curves are now correct. I'll let you know if I discover anything else that is off regarding attenuation levels. Thanks again!