Being in North America suppliers like Newegg and OWC should be convenient for you for standard stuff like drives and RAM.
The trickiest part would probably be the TV integration if your service has a smart card access control. It would depend of the smart card interface. If the provider allows standardized interface like a CAM (conditional access module)
you can use the EyeTV or Digital Everywhere hardware. They have an online store that delivers world wide. The Mac software is EyeTV which you can also purchase from Digital Everywhere at a discount.
http://www.digital-everywhere.com/en/alcms/index.php?sid=1190324464
http://www.elgato.com/elgato/na.en.html
If you have propriatory boxes only then it would depend of being able to interface with the box by Ethernet or firewire. That would be a second rate interface anyway because you would almost certainly not be able to control the box from your Mac Pro which is the objective.
Blu-Ray playback software is available from CyberLink PowerDVD or Corel WinDVD or Sonic BD. Usually a SW comes with your BR drive.
Ripping BRDs is possible with AnyDVD HD from
http://www.slysoft.com/en/anydvdhd.html I probably do not need to tell you that you need to observe your local laws about disabling copy protection. I my country you can rip BDs that you own to HDD for your own use but the legal situation is different across the world.
For sound interface your SPDIF I/O of the Mac Pro is probably all you need.
For graphic I would go to a patched PC ATI 4870 or an original Apple 4870 from the Apple store.
I do not use front row because I see not much benefit in it. YMMV