I have never experienced any issues with combining individual signals with a mux. The individual signals retain their original values after demuxing, and are displayed properly when fed to a scope. So I suspect there is something else going on here causing your issues rather than the mux. Note that you can also add additional ports to a scope to display multiple signals. Right click on the scope, select Signals and Ports and add the additional ports. If you are still stuck, please attach a self contained Simulink file (or a Simulink file and a .m file that sets all of the parameters so that the simulation can be run) that demonstrates the problem.