The difference on the QS4s is pretty pronounced, assuming you had the original original version. The v2 designation basically denotes an accumulation of changes over a few years; in crossovers, mainly, but some cabinet design and driver changes. The QS4s have had their tweeters replaced with ones that match the rest of the line--do you remember if yours had 3 screws in the face or 4? 4 is the new one.

I am the Doctor, and THIS... is my SPOON!