Everyone is certainly entitled to their opinion, and I do agree with some of what akg_ca says, however not this,
"especially for a 5.1 setup wherein the CC and RL and RR are a non-critical manufactured audio track"
This was true in the early days, but 5.1 today is 6 discrete audio channels. Above 5.1 (6.1, 7.1, etc.) is created using matrix processing.
The absolute best sound is created by using 5 identical speakers.
http://avtruths.com/speaker.html
http://www.soundandvision.com/content/matching-front-and-surround-speakers#GsU4hCQPZXlESVeL.97
IMHO, I would try to find another pair of Snells like you currently have and use them on the rear, a 4.1 system. Center channel will be set to none creating "phantom center". You don't lose any information as it just splits into the front L&R. This will sound fine unless you are sitting way off axis to the picture. Then find another pair of the Snells to use one as the center and the other as a single back surround, a 6.1 system. The only problem for the center is that you cannot place it too close to your TV. I noticed you are still using an old style TV, and the Snell will cause a problem with its picture because the speaker is not shielded. All dedicated center channels are shielded to prevent this. That's why I suggest 4.1 to start, and maybe by the time you're ready for another pair of Snells, you'll have a new TV. Then placing the center close won't be a problem.