I have been working on the same type of problem and it seems to me that you're only going to get the solution you are looking for (right now) by either using only one category. Seems to me that if you use more than one category in a matrix, you can only get each category's row and sub-row totals which is what you don't want. I had to switch my visual to a table (from a matrix) in order to get the view you show; but then you lose the nice category formating of the matrix (:.
You can't selectively turn off subtotals in the matrix visual. You either get subtotals for everything, or no totals at all. Those are your only options. For some reason they left this basic feature out. The best workaround I've found is to write a measure that produces some of the items you would use for the non-subtotaling columns, and use that in the values.
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I realise I am a bit late to the party on this discussion, but I recently needed to do something very like this, and found a different way to accomplish it.
My need was also to have multiple columns display the total - with several different measures etc. this meant I really needed to find a way for the matrix to provide this.
My approach was to make a 2nd copy of the matrix, then turn subtotals on, but to narrow the height of the matrix until ONLY the header and the Grand Totals row were displaying. This then meant I could place things where I needed to, display the grand totals, AND NOT the subtotals.
I did place the first matrix on top (in front) of the header row on my second matrix - which allowed a bit of ugly text leakage. This I fixed by placing a white box strategically in front of my 2nd matrix to hide the header row - but behind the 1st matrix.