Ok so while digging around on my hard drive I found out that I actually already DID put my effort where my mouth was and recorded these quite some time ago. They were recorded back when I did not yet have an external audio card so there is some ground loop related (I think) background interference, but you can clearly hear that it is identical to CS4236 in terms of FM Synthesis. It has the same warm, metallic cymbals and all.
I vaguely remember posting these on Vogons previously, arguing in support of the theory that CS4289 was in fact a licensed YMF289 OPL3 clone, but was proven wrong by Tiido (and maybe others?) that it in fact sounded different. It does in fact have the same package and pinout, though, hence the CS4289 name, and lack of a PDF datasheet. This IC was first integrated into CS4235, but it is well known that the integrated FM synth in that chip is broken, so we can safely assume Crystal fucked it up on their first try. That implementation was fixed with CS4236 I believe.
As far as I know the theory that you can replace a CS4289 directly with a YMF289 and get genuine Yamaha OPL3 is yet untested, but fairly sound. However, the YMF289 on the the Orpheus sound card is connected to the CS4237 in the exact same way CS4289 is connected to the CS4232 unless I am mistaken. That means, if you have SMD soldering skills (I do not) and courage, you could theoretically add OPL3 to a CS4232+CS4289 card by replacing CS4289 with a YMF289 chip. keropi is the expert on these chipsets and he could have more information, so paging @keropi 😀
Now that I have that card in a build again, I can make cleaner recordings with better equipment; so let me know what you want to hear.
