Convering bandwidth (frequency) to bit rate without knowledge of the modulation?
You haven't mentioned what the sampling rate is. According to the Nyquist Rate, you'll need to sample at twice the analog bandwidth to achieve alias-free sampling.

So assuming you want 60 kHz sampling, your total data rate will be:

60 kSamples/sec * 2 channels * 4 bits per sample = 480 kbps.