What version of Creative Suite: CS, CS2, CS3…CS6, CC, CC 2014?
I guess that would have been helpful. CS5. But I found another forum that states I can't use Adobe Camera Raw for my 6D with CS5 at all. I have to upgrade to CS6 to be able to upgrade to the appropriate ACR version. On the fence about springing for the $200 upgrade. Downloaded the DNG converter, but I can't figure out how to have it convert with my LR data intact before I pull into PS.
Programs by ACR version: Camera Raw-compatible Adobe applications
You should be able to update CS5 without getting an error which is ostensibly what this thread is about, but you are correct in needing CS6 to use ACR 7.3 which is the minimum version of ACR that supports the 6D natively. You can use the DNG Converter to make DNGs that the older ACR will read, but that has nothing to do with images already processed in LR, because LR knows newer adjustments than your CS5's ACR 6 does.
To go from LR to PS you'll need to use Edit In PS CS5 and when you see the message about ACR being too old, choose Render using LR Adjustments and Don't Ask Again if that is also an option. This will cause LR to render a TIF or PSD (whatever you've chosen in the External Editing area of LR Preferences). If you don't see a message about ACR being too old because you've selected Don't Ask Again previously then you can click the Reset Warning Dialogs button in Preferences and get a chance to answer the question differently if need be.