Assuming you mean to use these as satellite tuners for a Pi media centre, then not good.
Firstly, you need to know what the control protocol is. Looking at the company web site there's precious little info on the DVB-S2 tuners, and what there is looks wrong (Input frequency range：48to860MHz - this should be 950-2150 MHz for DVB-S/S2). There are no technical docs, just compliance info. If you can identify the exact model / part no for the tuners, you 'may' find a bit more info from a forum or group on the web, failing that you'd have to contact the company direct. Given that the most recent dated post on their site is May-2009, you may find they've moved on to other things.
Secondly, I2C can only control the tuning parameters to the tuner - its just not fast enough for video. The ouput will most likely be a 44Mhz (ish) I/F signal that you have to process. You'd need to decode, split and de-scramble the stream all on the Pi, this is not a simple task (you're talking encryption hacking here, which needs a bit more power that the Pi has).
Try searching the web for the model of STB you have though, you may find someone has already hacked it, and found a way to do something with the signal.