A random question about two Say You Will tracks

[KenshiMaster16]

Okay, so I've been a Mac fan since the late '90s and I bought Say You Will only after I saw them perform the tracks live in '04. So I've been reading up online that there are Center Channel Mixes, whatever those are, and special single mixes of Say You Will & Peacekeeper. Can anybody enlighten me on what exactly these are and what makes them different, or actually post them to download for me since I can't seem to find them anywhere else??