In the past I have tried Roland Virtual Sound Canvas (VSC) and the Yamaha S-YXG50 but all I've ever been able to find are trial editions - no place to purchase a license?
Support for them was dropped many years ago. They sometimes pop up on eBay, although I find the Virtual Sound Canvas has terrible latency issues.
I know that installing a software synth will work for Windows-based games but what about older Sierra titles? KQ4, for example. How can I get better sound through DOSBox? Can I use a software synth or would I need a hardware module?
DOSBox simply outputs to the MIDI device you have set in Windows, so software based synthesizers will work fine.