> since the card is supported in 2d, I would think it would come up?

With your HD5770 it's apparently the same as with the HD6450 and HD6570 mentioned before in this thread, which are also reported to work on the official list of supported hardware, but for some reason do not. It may be a case of unknown device ID, as the MorphOS graphics drivers use a whitelist and likely refuse to work with not (yet) known device IDs. There have been cases where the MorphOS team simply added another device ID to the whitelist and the corresponding graphics card which refused to work before suddenly worked with a beta driver or a new MorphOS release. It may be something entirely different, though.