Is BBBk I2S limited to 48KHz

Hello,
I’m using a BBBK Rev B with Debian 7.6 Image 2014-10-08.
I’ve connected a DAC PCM5102 (from DIYINHK) thru I2S signal (pin 25,29,30,31 on P9).
It works fine excepted it’s limited to 48KHz sampling rate (any other sampling-rate file is down or sampled).
I’ve tested it with alsacap (http://www.volkerschatz.com/noise/alsacap.c) and it confirms that 48KHz is the only sampling rate available :

*** Scanning for playback devices ***
Card 0, ID Black', name TI BeagleBone Black’
Device 0, ID HDMI nxp-hdmi-hifi-0', name ‘, 1 subdevices (1 available)
2 channels, sampling rate 48000…48000 Hz
Sample formats: S32_LE
Subdevice 0, name `subdevice #0

I’ve read in the documentation and misc documentations in the Net that higher sampling rates (multiple of 48KHz, and at least up to 192KHz) should be possible.

What’s the trick ?

Thanks in adavnce for any help.

Pascal