a quick look to the PCB showed, SONORO is using a PIC18F67J11 processor. Well, as an experienced engineer, you always have an ICD3 programming and debugging adaptor at hand.

To ease the hackers life, the silk screen of the PCB tells you where the programming port for the PIC18 is and which signals are where.

So, using the standard ICD3 tools, you can read the processors memory and search for the text shown on the display.

As the hex view of the downloaded firmware shows, the display text is stored in plain ASCII as part of the firmware. So you can patch it from "Aux 1. Eingang" to "Apple Airplay", write this new data  back to the processor and you are done.

Because SONORO does not seem to use any CRC or similar protection of its firmware, any modification is possible.