IAC IAC should always become 0xFF in Telnet emulation
vsid crash on some .mus/.str files.
Have you tried with setting the driver to output Mono? I've observed Stereo output behaving badly (2SID defaults to Stereo), and Mono working. I need SDL sound for the JS version of VICE, hence my interest.
SDL sound driver fails on Windows
xpet freezing in some circumstances