For coreboot there are actually some interesting low-level emulation options: The PCH has "I/O Trap" settings, where you can set about 4 ISA I/O ranges to be trapped (generates an SMI, so the SMM code can handle it), so it should be possible to emulate the Sound Blaster I/O port behavior.

I don't know if the trap mechanism allows you to also trap the ISA DMA ports, which you'd need to do for DMA emulation.

Slightly higher level you could use classic VMM or more modern hypervisor functionality to do the emulation.