The 6D was first supported in CS6 / ACR 7.3.
If you want to continue to use PS the way you do, now, then you’d need to upgrade to CS6.
You can also use the free DNG Converter 8.2 (or whatever is the most current) to create DNG copies of your 6D raw files that can be understood by older ACR plug-ins. Just make sure you set the compatibility options to older than whatever version of ACR you are using. I think this would be ACR 6.6 for you. You can download the latest DNG Converter from the Adobe Updates page:
Finally, the cheaper upgrade option going forward would be to switch to Lightroom which is much cheaper than Photoshop for upgrading. There are newer minimum operating system requirements so make sure it would work on your computer, first. You can download the latest update and run it in trial mode for 30 days, using Edit In Photoshop Elements with LR Adjustments as a way to do final tweaks in PSE after doing the main adjustments in LR:
The LR 5.2 update is available at the same Updates link, above, but the main Lightroom page is:
Message edited to correct downloads link
And of course there's the Photographer's bundle for Photoshop and Lightroom, which is arguably a good price for keeping up with the very latest Photoshop AND Lightroom versions.