The 43TX and 45TX use the same amplificatoin section as the current 53TX and 55TXi and were known for not being very friendly to 4ohm loads. If just your mains are 4ohm but bi-ampable you could probably get away with using the back channels to bi-amp. I power my 4ohm Swan's Diva 4.1s in a similar manner, the individual binding posts present nominal 8ohm loads individually. I haven't had any problems, but I haven't tried using JUST the front channel of amplification in a non-bi-amp configuration.
I would guess that the ML's are a bit more difficult to drive that just your average speaker. I am not saying the Elite will not drive it, but I don't think it, or most recievers for that matter, will do them justice. If the Elite has pre-out you can add an amp which will help, but then if your spending that kind of money, you have other options.