Problem with setting AD9361 bandwidth using libiio

We are trying to transmit a signal using the AD9361's full 56 MHz bandwidth.  We are using the libiio/py-adi library for configuring the device, and we set the following field in both the C and Python versions of the code: txcfg.bw_hz = MHZ(56).  However, when we measure the output of the transmitted signal using a spectrum analyzer, we observe a spectrum of 2 MHz.  Should we be increasing the sample rate of the DAC to 56 MHz as well?

Thank you.