I've currently got three separate XT-IDE controller cards + HDDs that all work in my PC10; the one that originally came with it, plus two others (a SCSI and an IDE) which I pulled out of Sanyo MBC-675s.
From the PC10 manual, jumper JMP 208 should be in the A position if you're using an external controller (in an expansion slot). It should be in the B position if you're using the onboard controller and connecting a drive directly to the motherboard header (e.g. an A590). I understand you would also need to set a jumper (or switch) on the A590 itself to change it from SCSI to IDE.
However, as I already mentioned in a PM, I'm looking to upgrade to an XT-IDE
card when more kits become available.
Also, from what I can gather, CF memory cards might work with the onboard controller since they're XT-IDE compatible.