If your emmc is not working, I don't think you can. My understanding is that these amlogic boxes basically are hard coded to look for uboot on emmc. That is why the aml-s9xx-box builds use the emmc uboot to then chain load the distribution from sd/usb/etc. It is always using the emmc uboot initially. If your emmc is working, you should use recovery to reinstall the android uboot and then you could move on from there. But in your case you have already tried that, and it didn't work (likely indicating that your emmc is not working). Based on your comments, it sounds like you have previously reinstalled the android firmware, so you know that process used to work (the reason I am stating this, is that sometimes different boards/firmware combinations require specific versions of the amlogic burning tool)