Good news! The OPL3 emulation code is making great progress - with this java code as a base, integrating the log-sin discovery, reducing the floating point math to simple bit manipulations and great help from this forum, I finally managed to get some pretty good results. You can directly compare a real capture and the emulated output (left is emulator, right is youtube). But the code is still in an early state and it will probably take some time until it is ready to be released into the wild. Unfortunately, I don't own an OPL3, so I have to rely on the captures of others, but these others are hardware guys and have much better knowledge of how hardware is working.
The final words: I will release the OPL code under the LGPL so that it is easier to be used in other projects (I'm thinking especially of DosBox and ScummVM).