I don't think you can assume your optical drive is working when 4/5 different disks all failed, sounds like your troubleshooting the right stuff but without knowing if the stuff your connecting is known good its all a waste and hypotetical, you need a known good bootable disk (optical or magnetic) and you need to try booting from that, it sounds like there is a problem with the optical drive and thats whats stopping you from using it to fix the hard disk. I suggest you get those disks in another mac to test them or use a firewire cable and target disk mode to use another mac's optical drive to boot.