When you say you have a simulink block with two buses, do you mean you have two bus signals, from which you'd like to select the "x1" signals from each?
If so, you can do this by just using 2 "Bus selector" blocks, and selecting "x1" from each of the bus signals into the bus selector.
If the above does not reflect what you are trying to do, can you go into more detail on specifically where these bus signals are going, and which block you are inputting the two "x1" signals to?
