Some peculiarities with the sample rate returned by the API and also visible in the MusicBee UI:
1) Missing accuracy in kHz
Actual file sample rate -> API sample rate
11025 Hz -> 11 kHz (missing accuracy)
19999 Hz -> 19 kHz (missing accuracy)
20000 Hz -> 20 kHz (correct)
20000 Hz -> 20 kHz (missing accuracy)
88200 Hz -> 88.2 kHz (correct)
2) DSD files report different number separator and kHz/mHz mismatch:
DSD64 -> 2.8244 mHz (correct)
DSD128 -> 5,644 kHz (wrong number separtor, wrong unit)
The above examples can be viewed as a bug or be solved through additional API entry for precision sample rate in Hz.