To install AROS in UEFI is a bit tricky. Tell me if I'm doing it well: I launch the AROS Installer on an EFI enabled instance, wipe the disk with EFI enabled, then reboot, relaunch the Installer and directly install AROS without touching any setting. Once done, I format the EFI drive with the Wanderer format menu, naming it EFI. I copy the efi directory from the CDROM to the EFI: drive (doing this, I have now an EFI:efi directory). I navigate to EFI:efi/BOOT/grub and open a shell there. I then edit the grub.conf file to add: "root=(hd0,msdos5,amiga1)" just before the multiboot2 line. Save, reboot.