TheOptimizationIdiot - 9:45 pm on Apr 11, 2013 (gmt 0)
I'd wait to move the .xx to the subdomain and go with exactly what Robert_Charlton said, except to go to the new URL structure initially. (And, the way he suggested might actually be better, but I would personally go "to the final location" from the start.)
I think it's very important to understand: Patience is definitely a virtue when moving domains and doing things slowly, methodically and patiently are the best ways I've heard or found in the years I've been doing this.
By being patient, you have a "known traffic level" to at least one of the domains and you can fairly certainly count on that level while you're moving the .net site.
Then when traffic to the .com gets to the level (or close) the .net was at you will again have a "known traffic level" to at least one of the domains you can fairly certainly count on.
If you rush and move both at once, then something "goes wrong" with the move you can be completely and totally hosed for any traffic at all to any site you have, and like it's been said here over the years... "You can't uncook an egg.", so once you move, reverting for recovery might not be an option.
I'd definitely recommend, a careful, slow, methodical move of any site or set of sites these days, unless you can afford a total traffic loss if something goes wrong.