You should be able to get a symbolic solution - makes no difference what the values of the parameters are. They don't come into play at all. After all it is just Cramer's rule. Having said that, note:
1. You have 6 equations in 5 unknowns so you wont get a symbolic solution.
2. The Symbolic toolbox is S***. Unmentionable word here. It will take you some time to get used to its quirks. Plus the confusion between the Mupad documentation and the matlab - the syntax is totally inconsistent. Best of luck trying to use it. I have written a few m-files to construct and solve some specific large linear systems. Works, but the frustration is not worth the effort.