You'll need to google the PS2 emulator's name, the BIOS path might be something like /mnt/sdcard/Android/data/made.UP.name/BIOS
I've had some success with RetroArch and Mupen64 Plus AE. RetroArch requires some configuration to get up and running, and I've only used those two on my phone, not a DroidBOX yet.
You should find them both easily via Google or the Play Store.