I assume "TS-RDF8W" and "TS-RDF8K" refer to either the white or the black reader.
I further asssume you downloaded the Mac version vice the Windows?
I think you're safe to try an install. OTOH, what is the 'update' supposed to ... 'update' or 'fix'? 
"If it ain't broke..."
Of course, you're the one who installed 11.6 already...

The firmware may not even be needed. Does the card reader work ok? If it works fine, I wouldn't even bother with the firmware updete.
FWIW
Jack
My thought exactly. I asked Transcend tech support that question and I'll post back when I get a response.