Hi. There is not version option in the Photoshop "save as" window. CS6 is a very old Ps version. If you have a simple image maybe you can open it in CS6 without problem but if you have an image where you use recent features of Photoshop, you could have issues with older versions.
Others have provided some great advice. Because it sounds as though you are dealing with some non-raster-based layers (logos), you may find that you need to rasterize these layers to be backward compatible.