I’m a moron.
I accidently named the Ambika controller firmware binary VOICE1.BIN and did (attempted) a firmware upgrade of a voice card via SD card. Now, this sound card seems to be bricked, i.e. it does not accept an install/upgrade of the correct voicecard firmware (via SD card) anymore.
Does anybody know if there’s some way around this, or is the only option disassembly, and flashing via ISP?