The current version of the XL only supports 44.1K and 48K in AAX DSP mode.  If you're using higher sample rates, you'll need to switch it to native.  This may change in the future, but for now, keep in mind that the XL is mostly meant for mastering, and of course in a mastering scenario there's less of a need for the ultra low-latency monitoring that you get with AAX DSP.