Just a thought Emiliano,
Try using an old G5 with a RAM disk. If all you're running is a single output, it should work fine. I have a venue with 2 G5 Cats that are running HD with no problem.
For the cost, you could have G5 2 machines (primary and backup) so long as your volume of content isn't hugh.
Memory on a G5 is cheaper per Gb than Mtron.