The SD CEO's comments on the 788T and heat (nit just a link):
"All that processing power generates heat. The numerous “systems” in the unit, such as its wide bandwidth analog circuitry, low-noise A/D and D/A, and the powerful DSP processor generate heat. The primary cooling mechanism of the 788T is its aluminum top and bottom panels. Any electronic component drawing appreciable power (ie. generating heat) is thermally bonded to these aluminum panels. This construction efficiently wicks heat out of the unit and keeps internal temperatures cool. In fact, the 788T runs nearly 10 deg C cooler than the 744T while having twice the I/O. While the 788T is designed to operate in extreme temperature environments, the cooler it runs, the longer lasting it will be.
When in operation, it is very important that the top and bottom panels have a bit of ‘breathing room’, especially when operating in a bag. A production bag filled with a 788T and numerous wireless systems and insulating (foam) dividers keeps heat in, rather than allowing it to dissipate."
If we can believe Tatooles it is designed to run hot, it runs cooler than the 744T and should not be run in a closed bag.
FWIW I recorded six tracks at 24/44.1 at ambient room temp 70F.
There was no appreciable heat on the unit. It was not run in the sunshine. It was not run inside a bag. It was run on top of a wooden table. I have not noticed appreciable heat in other instances. It seems the heat problems posted to the SD board are all about 788T's in a bag with little or no air circulation. They are, therefore effectively insulated from cooling, swaddled in the bag as it were.
As I have not ever used a Nagra of any flavor I keep my mouth shut on that subject.