I've tried both, internal and external, my FW is 3.55, i have a bd inside and tried the bd mirror option with multiman, although i get this:
"An error occurred during the start operation (8001003c)."
Thats why I recommend to at least upgrade CFW to something better like 4.21 or above as games now have other files encoded for above 3.55. All I did was re-encode the eboot.bin for 3.55 not any other files which I'm guessing there will be more files that need a higher firmware.
Its so easy to upgrade and downgrade so get a newer CFW and upgrade and play the new games. If you dont like that newer CFW then downgrade back to 3.55 and keep on patching all games.
As I patch the games myself I have no problems staying on 4.21. Even BF4 works for me with an easy patch.