I agree with John. The QS8s would be a great next step. The 60s will give you more bass than your current speakers and the JBLs will be too directional for surrounds. Next I would go for a sub while continuing to use the "phantom" center provided by the 60s and the receiver. Then complete the set with a center.
You also might not be aware of a couple of discounts that could change your thinking. There is a "Factory Outlet" from which you can buy discounted speakers that are funtionally perfect but have "flaw" in fit'n'finish. Most people who have bought FO products have never found these supposed flaws, including myself. Also, if you buy 5 speakers (any mix) at once you get a 5% "Home Theater Discount." So if you just bought new M60s you would pay $960. If you bought a pair of 60s, a pair of QS8s, and say a VP150 from FO your total price would be $1615.95. That's a pretty good deal. For comparison, buying this at full price would cost $1795.95 and buying them a piecemeal at full price would cost $1890.00.
