I am total newbie, but I always thought all sound cards sounded the same (as far as FM is concerned). Am I to understand there were soundcards who had better FM sound? For example, a sound card with an FM quality similar to the Yamaha PortaSound PSS-680/780?
The OPL2 and OPL3 output in digital, so it's more to do with the DAC used on the card.