Although, the SiI3132 SATA controller card is listed as compatible, my system crashes when the MorphOS boot loader shows up.

This picture shows the errors when booting MorphOS 3.19, but it's the same errors with Morphos 3.20 which has boot loader 1.17.

Any idea what's wrong here?

You can see in this picture, just before the error occurs that you can press Enter to select a boot source. But that doesn't work anymore, it crashes immediately so there's no time to press Enter.
I guess this is an issue someone from Acube or bigfoot has to look for.

That's interesting, just today I tried adding a Sil 3132 PCIe card to my PowerMac G5, and MorphOS wouldn't finish booting (the Mac froze).
I was thinking of using this controller with a new SSD, but I've put that on hold for now.

Thanks for the feedback. This can be an issue with a particular card, or the SiI3132 compatibility in MorphOS in generally broken.
The first two(!) SiI3132 cards I tried even crashed my system immediately so that I wasn't even able to boot AmigaOS. So I ordered the exact card that was confirmed to work on my system (with AmigaOS at least).