I don't think I would be too concerned about heat issues, unless you're practically burning your fingers in a second if you teach it.
Granted, a DAC doesn't have to do quite the amount of raw calculations as eg. a PC or a game console, but on the other hand the DACMagic doesn't have a fan or several to keep it cool either, so I would actually expect it to get well above room tempature during extended use.
Mine does. Or perhaps I should say mine did - I haven't checked how hot the new replacement I just got yesterday gets, and since I needed a replacement, perhaps I shouldn't entirely rule out that the first DACMagic I had actually did die of heat stroke

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