Stay away from QS4 and QS8.

The M3 sounds very similar to the M50. M5 bookshelves will give you deeper and more linear bass, clear mids and better lower highs.

I really think you ought to try M60s up front instead of M50s. You'll get tons of good bottom end and wonderful mids and highs to boot. They'll work well with your old receiver. M60s vs. M50s is a better upgrade than an ADA-1000.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated