Use Steam's Big Picture mode for HBO Go, Amazon Prime, etc. Create firefox profiles for each site (i.e. one profile for HBO Go, one for Amazon Prime, one for Starz Play), then, under each profile, set the appropriate site as the homepage. So if you launch firefox under the HBO Go profile, it'll open the homepage to HBO Go. If you open firefox with the Amazon Prime Profile, it'll open the homepage to Amazon Prime. And so forth.
You can use command line options to select which profile firefox opens with. i believe it's something like "Firefox.exe -p "HBOGo"" off the top of my head. Create some batch files that send the command to open Firefox in specific profiles. Example: You'd have an HBO Go batch file that would open Firefox using "Firefox.exe -p "HBOGo"" -- make sure to use the proper start command to launch this application, refer to windows batch help online if you don't know the command.
Next, use a program like batch-to-exe to turn your batch file into a stand alone launchable executable, then add them to steam as non-steam games. This will give you icons in Steam's big picture mode that will open to these streaming services. Ideally, you should be launching XBMC from big picture mode as well - BPM is your overall shell for the entire operating system in this instance. If you open XBMC within steam's BPM, the BPM overlay follows (i.e. pressing the guide button on the controller overlays BPM onto XBMC) which gives you access to friends lists, a webbrowser, etc. If you open your firefox profile executables through Steam BPM, the BPM overlay follows onto firefox as well.
For controls, I use a gyration MCE remote:
This is a universal remote with a learning function - so it controls my sound system and my television, as well as my PC. It connects to the PC via USB dongle which makes windows see the remote as both an MCE remote (for the media buttons at the top) and also as a keyboard and mouse, so you can boot your PC with no proper keyboard connected if needed. Using the freeware program EventGhost, you can remap any key on the remote to any sort of mouse or keyboard function.
Best of all, the remote is a gyration mouse - press and hold the button in the middle below the windows gem and moving your hand will move the mouse on your screen, much like a wiimote. To it's left and right are buttons representing left and right mouseclick.
I typically map windows+tab+ctrl to the green windows emblem on my remote, which does winflip 3D on windows 7, which is sort of my cool, nice looking way to flip between applications running without needing to use the start bar. The Ctrl modifier to the win+tab shortcut makes it so that you don't have to keep holding win+tab to do winflip 3D, making the button act like a toggle. Windows 8 kind of fucked that up by getting rid of winflip 3D, so I use switcher, a free program, as it's replacement.
I have a NAS drive in a raid-1 configuration elsewhere in the house that actually serves all the media. I have a few HPTCs that work like I describe, actually, with 3 different Gyration MCE remotes for different rooms. They all are served by the same NAS drive.
This gives me the absolute ultimate media experience. Absolutely nothing comes close. I can play absolutely any type of file, without needing to transcode it, and I can use every single streaming service around, without any sort of device restrictions. I can even get around ESPN3 blackouts by using a proxy. The UI is far more elegant than any of the consoles, with immediate task switching and true multitasking via winflip3D, and a persistent BPM overlay that follows me from games to the internet to XBMC to streaming services to anything else, at the push of a button that gives me friends lists and webbrowsers.
