: I have an extra (old) 360 I'd like to have my buddy use when he comes over to
: pew pew. We both own all the DLC maps on our respective primary consoles.
: If he were to recover his XBL profile on my 2nd box, could we download the
: maps on that console and not be charged?

Yes. And you could use them so long as his profile was signed into Xbox Live on that console.

: His primary box, at his house,
: would not be running the digital media at the same time.

Doesn't matter unless he's trying to be signed into his account in two places at once. Then I think it'd kick one of the consoles offline.

: Once he would
: return to his home console and recover his profile, I'm hoping the maps on
: my backup console would become inaccessible.

I do not understand the sentiment. The only way to retain access to the maps on your second console would be to have him transfer all his licences to it - making it his primary console as far as XBL is concerned. But I don't know why he'd do that.