PCITV should work on the Iyonix with any graphics card that has its display memory accessible via the PCI bus. At the moment it specifically searches for an NVidia card but it could easily be altered to search for an ATI card, for example.
Did RISCOS Ltd give any details on the NVidia issue that was mentioned? Source code to set up mostly any NVidia card is fairly abundant on the web. I don't see why they should have a problem. Perhaps this is another excuse.