APX has capability of software AES encryption now. I believe single slot though.
Correct; they used to offer single-key ADP on each radio but got bit due to the Federal requirement to use AES256 if you're spending grant money on the radios. Customers screamed and Motorola (amazingly) changed up and made single-key AES their standard free offering instead of ADP (which now costs money). The real big bucks come when you need multi-key encryption (several hundred $$ per radio).
Harris has been offering your choice (AES, DES or ADP) for 1 cent when you buy a radio for several years now. I spec all our stuff with single-key AES and Link Layer Authentication now.