The command would probably be the same as long as Xyce was in a directory that is on your shell path.
Note that most of your shell initializations are not run when MATLAB invokes a shell, because the invoked shell is not interactive. https://www.mathworks.com/matlabcentral/answers/27762-executing-unix-commands-set-in-path-in-matlab-does-not-work-with-unix-command#comment_194290