How do you think it will soundGrrrreat

��seriously I think you�ll be very pleased.
Not familiar with your speakers but don't sweat the 5.1. To me it�s like the difference between (quality of electronics parts used by various manuf. taken into account).
Composite to S-V ( a larger improvement)
and S-V to Component. (less drama to the improvement yet DOES make a noted difference)
Or like putting a progressive DVD player on largish display (practically required) or adding one to a smaller display (not so noticeable improvement).
I feel the speaker (count) is not as enormous an improvement to your SS as it is when you revamp.an old PL receiver and upgrade to something like the 950. I just personally perceive it as a smaller net gain when running 6.1 or 7.1 (over 5.1).
I have however a VERY small space where speaker distance is too tight (overlap) . I suspect someone with a cavern for a HT room , would realize a greater gain from 6.1 or 7.1. (just more seamless surround).
The 6th and 7th
do add to enjoyment, - but this can also be recording (material) dependent.
By the way Welcome to Outlaw!