A helpful Be engineer provides the following information:
As of BeOS 5.03, there are two SB128 issues. One is that the sound „crackles“ after some time and you need to restart the media server. This should be fixed in a future release of BeOS.
The other issue is that models 4750 (and possibly 4810) don’t make any sound at all. It appears that, at least for the 4810, booting into Windows first kicks it into a mode where it works. SB 128 model 5803 has been reported as working.
Also, there are some VIA-based AMD motherboards for Athlon and the newer AMD CPUs, which don’t produce sound at all, even if the same sound card may work on a different motherboard or an Intel-based chipset one.