Ah, OK. So here's the worst part...
Since the Sabre32 runs at 32 bit precision internally, it doesn't have to truncate in order to attenuate even a 24 bit input. I don't recall if they use floating or fixed-point math for this operation but even at fixed point one should be able to get at least around 50dB before truncation. Also note, everything will be attenuated, including the noise floor of the recording. In practice, you'll be limited by the analog noise floor of your system long before you're limited by internal precision on the DAC. Thanks to the exceptional SINAD of the ES9012/18, you could probably get at least 10-20dB of attenuation without significant loss in dynamic performance at its output (so, then, it's up to the rest of the system to keep up). On the other hand, with an analog volume control, additive noise will go up as you attenuate in addition to other potential maladies (e.g. crosstalk, distortion, and so forth).