I would love to use OSSv4, since the built-in oss doesn’t support my sound card properly, but the oss port didn’t build on FreeBSD CURRENT or TrueOS the last time I checked. It is incompatible with pulseaudio though, which has sometimes caused me problems with KDE applications.
Does SNDIO use the built-in, FreeBSD kernel drivers, or does it use its own drivers like the oss port does? As far as I can tell, there has been no progress in the FreeBSD sound drivers for a while (comparing the HW compatibility list for soundcards between releases, it basically doesn’t change). Maybe the OpenBSD guys have been doing better on that front, since they seem to care more about desktop machines? I don’t know, but I can hope. It’s a moot point if SNDIO just uses the built-in FreeBSD drivers though - though presumably, if the OpenBSD guys had already gotten working drivers, it would be easier for someone to get them into FreeBSD. FreeBSD is so behind on sound drivers that I don’t think that it supports any PCI-E sound cards in existence, and I don’t think that it properly supports many of the USB sound cards. I’ve tried to find a sound card that I could buy which would work with the built-in FreeBSD sound drivers and have found nothing except maybe some ancient PCI cards that won’t even work in my computer, because they’re PCI and not PCI-E. For a while, oss worked as a workaround (though since you have to build your own kernel, and it doesn’t work with the stuff that requires pulseaudio, it’s still far from ideal), but now, unfortunately, that isn’t an option anymore.