I just got my Tvix 4000SA and after an hour of use, the top of the box feels quite hot to touch. Is this normal? I saw this and increased the fan speed but that doesn't seem to help.

My system has no hard disk inside, I'm playing off an external USB drive if that matters.

I have a 4000SA too.
For me, I only play mp3/movie using internal HD (western digit).
The unit's heat is "normal" after 2 - 3 hours operation.
(my hand only feel warm, not hot).
Fan speed is set to default, I place the unit next to my LCD TV with nothing surrounding it.