A lot has happened in the meantime, and at least now, emulation has reached a very good level. OPL-2 and OPL-3 synthesis in DOSBox sounds pretty authentic, it has instantly taken me back, even when directly comparing against original recordings. MT-32 is a tough nut to crack, but Munt has made a lot of progress as well.
Both DOSBox and Munt are active open-source projects, so those who are not happy about their authenticity are encouraged to participate in the effort! People who have long experience with and knowledge about how the originals sound are exactly the people needed to take the emulation to the next level.