"Naturally a vacuum presents no obstacle to EMR. Heat (actually, energy which only becomes heat when absorbed at the other end) can easily be transmitted across a vacuum using EMR."
I see a couple of inconsistencies here. Granted I am not an expert, but my understanding is that an object cannot possess heat, therefore EMR, specifically Infrared is heat because it IS in transit. When it reaches the other process it again becomes Temperature or internal energy. The last of your statement that "heat can easily be transmitted across a vacuum" via EMR contradicts your previous premise that
Since a vacuum is the absence of matter, heat conduction cannot take place through a vacuum, and therefore a vacuum is a perfect insulator". A perfect insulator resists the transfer of any form of energy. And even if we were to limit the statement to "Since a vacuum is the absence of matter, heat conduction cannot take place through a vacuum, and therefore a vacuum is a perfect thermal insulator" infrared radiation is a transfer of energy and, therefore, heat.
This has been an interesting read so far. I know I will have to do some brushup on my physics, but I'll be back
Thanks