It was just 56k. I seem to recall back in the day people appended the ".6" for no apparent reason other than it sorta seemed logical after we had 14.4k, 28.8k, 33.6k, and then.. all of a sudden.. 56k.
(and, if I recall correctly, for technical reasons it was really only 52k, and even then, only if you were lucky, usually it was less.
I seem to recall that the equipment was theoretically capable of 56k but in actual implementation, even a perfect POTS system wouldn't do over 52k, and in the real world, it would usually negotiate lower due to distance from CO, quality and number of connections and equipment in between, etc).
Neither did I! And I'm a bit humored to see other people pronounced it like that too :) I wonder what causes it, regional dialect or something? I'm part-Mexican, grew up bilingual and it just sort of happened without thinking about it, I discovered 'warez', immediately pronounced it "Juarez" (without the Spanish jota inflection) and it took 30 years (today) to learn it's 'wares'.