GJ, welcome. Even with surrounds it's a good idea to have them not be greatly different in sound quality from the mains. The CM9s are fine quality units and in my view the QS8s are as well and don't differ to a major extent in timbre. Any small differences would be more than offset by the superb spacial characteristics of the QS8s and you should be very pleased with the overall effect.

-----------------------------------

Enjoy the music, not the equipment.