That is true for the early Beovision models - I believe you can display an image from the DVI input via the PC input, but the component inputs are not enabled and sources are not assignable to the HD inputs. Others may know which type numbers and software levels allowed HD inputs on both inputs for the Beovision 6.
I'm pretty sure all of the Beocenter 6 models were HD enabled from the factory (others can correct me if I'm wrong). I have a Beocenter 6-26 and can confirm 2*720p inputs are possible via DVI and component. I still think it's a great little telly with a useful size (I'm not a fan of big screens, but thats a personal choice). The picture is okay, but isn't a patch on modern LED sets of similar size - the main reason to keep it for me is the master link integration with the rest of the house, and my master link gateway (note you need the very latest software to pass light commands to a MLGW).
Unless you get a late model HDMI enabled Beovision 6 then there is only one STB controller available (and no STB controller if you get a hotel version, although it is possible to remove the business to business module in the hotel version and enable the STB if you are brave enough to open it up and remove it.)
The Surround Module was an optional extra in the 6 range, so unless it is specified as an accessory you will only have the option of 2.1 sound (with the centre channel in the Beovision itself, and 2*powerlink outputs for stern left and right). Apparently the surround module was identical to that of the earlier Beovision 3. I actually got hold of one and installed it in my Beocenter 6-26, but was never able to get it to work correctly.