Don't bother with rears. Human ears are relatively insensitive to sounds from behind. Sell them or trade them in. I had rear QS8s as well and traded the sides and rears for a pair of QS10. It doesn't even feel like I need Atmos. I hear the dragons from Game of Thrones beside and above me.

Trade in those M60s and run to buy M5s. The M3v4 sound better than my M80v2 and the M5s are manna from heaven! Read my M5 review on the second M5 product review page. No need for height or width speakers either with the v4. No need for simulated surround like PLII either for music.