I've just bought one of these. The BD-D8500 has two tuners but you can only record from one channel at a time. An "interesting concept" from Samsung.
The only use I can think of for the second tuner is for timeshift viewing one channel while recording another, but I'm not yet sure whether even that is possible as I've seen one reviewer state that "only one tuner is attached to the hard drive".
I knew about this rather bizarre limitation before buying, and everybody else needs to know too.
There is a DigitalStream product on the market that allows you to record two channels and usually watch another, all simultaneously. I tried one of these. Functionally it was excellent, but the picture quality was not as good as the Samsung BD-D8500, and it was a bit of a pig to use. Plus, I wanted a Blu ray player all in one box, so the Samsung fitted the bill for me.