Aviator is on the money. Forget any version of the 256 - they are basically flawed.
The MAG 256 is best avoided. We pulled the plug on supplying these as experienced similar problems with heating and reliability - Informir denied everything, but we have sales staff in different countries, all reported the same. Avoid.
MAG 322 thus far, seems ok - though we do supply these, we have also found alternative models which presently seem a little better - faster/smaller - but cannot give too much away
Of the Infomir boxes, the 322 is likely to be the best option - though overall, over the last few years i've not been too impressed with the MAG hardware - the user interface is good, but the units themselves are a bit well, MEH..
The 322 does NOT have the vents underneath as the older 250/254 - so in that respect (possibly unwisely) is the same as the 256 hmmm. Having said that i've not seen a broken 322 yet after a few months and office test box is ok, still a little wary about their product testing/quality control.