Yes, you could try the QS 8's, because of the 30 day policy. I have heard center channels sometimes sound good as 6 and 7th speakers. I believe it was canadian_guy that suggested this.
If your speakers are causing the bad panning, they are likely really bad at imaging and being transparent. Do you ever use them in two channel audio? this might be a good test to see if they have these traits. My M3's have a great soundstage, and some pretty darn good imaging for what they are. They disappear in my living room. I assume M50's would be even better!