Harry, welcome. The problem with just about any question that has a "vs" in it is that unless someone has compared the two items in the same place at the same time and with everything else as near equal as possible, any comparison isn't really going to be accurate. In this case, very few have heard the Def Techs(I haven't)and probably nobody has been able to make the sort of simultaneous comparison that I described.
As you apparently have already read, the QS8s are extremely impressive performers and you almost certainly won't be disappointed in them and can be confident that you made a good choice. As to how much better than the Def Techs they'll be, you're going to be the judge of that and hopefully you'll let us know. Your 4308 is certainly an excellent receiver and I'm sure that your setup will sound great.
