Moving from 2 drives RAID 0 to 3 drives RAID 5 is it possible for your chipset type.
This information is confirmed here: Intel® Rapid Storage Technology (Intel® RST) — Supported RAID Migrations
Please bear in mind the C600 chipset model belongs to an Intel server platform, for instructions about how to migrate your existing RAID volume, I recommend contacting your computer manufacturer or motherboard maker.
If you have an Intel(R) server board, please address this matter here: Servers
yes I have found much information indicating that it can be done, but what I haven't found is the step by step how