Hi Chris,
Ravi is correct about locating two QS8 surrounds to the sides of the listening area, as Dolby Labs intended, and I'd opt for two additional QS8s for the legit "back" speakers for 7.1. Despite what you read, it's my experience with multipole surrounds that there is no loss whatsover of directional cues with either home theater or multichannel music. Besides, you'll get better timbral envelopment using four identical surrounds rather than mixing two multipolar surrounds with two direct-radiating speakers.
Regards,
