Santiago,
I felt your problem was likely to re-occur because we did not actually track down the cause.
Based on the information Henry supplied I feel he had a very different fault which was clearly a faulty speaker.
In my view your situation is very different and I think we need to recap where we are fault finding the problem, so lets restate the facts as I have understood them:-
1) The pair of Beolab 3's are brand new and all supplied cables are used.
2) Both speakers are both exactly the same high temperature after about one hour.
3) The Beolab 3's took the place of Beolab 4's which had been working perfectly.
4) When running the Beolab 3's for several hours in the bedroom, they remained totally cold.
5) Your home is about 6 years old and never had any power related issues before.
If I have understood everything you have said correctly, then I still feel you have a power or earthing related problem.
If your dealer does decide to replace the Beolab 3's, I feel those new speakers will still get hot unless you were very unlucky and had two faulty speakers with the same problem, possibly caused if it were a manufacturing issue. One way you could be sure if you have a power/earthing issue is get a one-to-one mains isolating transformer and power the speaker via this isolating transformer. If your speakers still get hot, then the problem is almost certainly two faulty speakers with the same problem. If, however the speakers remain cold in use then you know for certain that you have a power/earthing issue in your home.