I would suggest M60, VP160, QS8s and EP500.

The VP160 is the best upgrade over your original thinking, it will play equally with the M60s, the VP150 is good with dialogue but I found you miss impact from the front with the VP150. The VP160 does everything.
You could get away with QS4, nothing wrong with them, but the QS8s match the rest of the driver scheme and have the same tone.

And the EP350 is a great sub but the 500 does play a little lower and it is noticeable on certain movies with good LFE soundtracks.
_________________________
Jason
-----------------
TTTHHHPPPPPTTTT!

My HT