Yellow head jawfish are amazing...they are beautiful and have great personalities. I think you might be okay with three in a 55 gallon, as long as you have a good sandbed and plenty of room for them to make their burrows separately from each other. And who knows, two could pair up, or not.
Again, perhaps someone could shed some light on their experience. You might want to ask the reef forum about that, though. And if you're going to have jawfish, you can't have aggressive fish because they're easily bullied. Also, make sure you have a tight fitting lid because they can and probably will jump.
A snowflake eel would be good to have in a 55g, particularly if you have a small one. I used to have one and she was quite charming. Although they can't be kept with any invertibrates or small fish, because they will eat them...or, at least I know that mine ate a basslet and a filefish. They need to be kept with other aggressive fish, which you've been talking about. That might work better if you want to do an aggressive set up.
I hope this helps.