I'm not 100% about tire track eels but I think they are a little more aggressive than fire eels. I would expect that as it gets larger it might become aggressive towards some of the other fish. This probably wouldn't be a problem with normal tankmates but you have discus, angels and silver dollars, all of which are easily stressed and will most likely be stressed to death by the tire track eel at some point, given the size tank they're in. Also, I would definitely worry about your tire track eel swimming into the overflow. If you've already lost a fire eel that way then I wouldn't expect any different with the tire track eel.
The silver dollars will probably eat your plants eventually. Also, I recommend getting rid of the silver dollars because they are fast darting fish and that stresses out the discus.
I really think replacing the tire track eel, peacock bass and silver dollars with 4-5 more discus is your best option. It will keep the discus comfortable and at that point you shouldn't have to worry about anything outgrowing the tank.