The "Kirby" system mentioned above works very well. You can use any couplings you like as long as the hooks themselves aren't magnetic. This rules out the Hornby ones as you say but, in most cases, it's fairly easy to change them. Obviously, if they are in NEMpockets, it's a simple matter of pulling the Hornby ones out and slotting Bachmann ones in. If you have stock with the older style couplings, Bachmann have a number of coupling options that are a direct replacement once you've removed any rivets etc that retain the original couplings. The new ones can either be glued or screwed in place.