Depends on your goal.
If movies are your goal, then the rear surrounds are not really that critical. They are usuallly reserved for SFX, occasional mood music or atmospheric ambiance. None of which really requires a critical match to the front.
If multi channel music is your ultimate goal, then the rules change a little. An engineer/artist can mix whatever insturments/sounds/voices into whatever channel they wish. They are not limited by sticking to the requirement that all "music" eminate from the front. I'd say for this application, matching would be more critical.