It is a Windows issue in general, not a Windows XP vs 7 issue. This is more to do with the way the Windows audio subsystem works where changes made in Vista would have Windows 7 being more likely to support this feature than XP. Kind of something you have to learn the hard way most of the time, but there are plenty of people who will claim XP was better at everything. There are always some who pine for days past, remembering only the good things and ignoring the bad. Like how the 1950s is frequently thought of as a golden age in the US, except it was rife with racism and gangs were running rampant. So whenever you hear someone claim XP was so much better at everything short of serving you coffee in the morning, take it with a good sized grain of salt.
Your one and only hope in all of this is finding a program which doesn't just use the default audio output device, but can be manually pointed to a specific output device. Such programs are rare and I'm unaware of any program that can output the same signal to multiple ports simultaneously. I suppose some professional DJ software might be able to do it, but I know next to nothing about that entire genre so I could be dead wrong on that. What you want to do isn't even generally possible with dedicated hardware like surround receivers.
If you can find three programs which will let you manually select an output port, you can try having different instances pointed at different outputs. It probably won't work, but it seems at least worth a try. I'd use different programs, since separate instances of the same program will likely clobber one another's settings. MPC-HC is one program capable of this as is XBMC. I believe VLC Player is also capable of it. So you could use MPC-HC and VLC Player as the secondary programs and XBMC as the primary. Just don't be surprised if it doesn't work. And stop listening to fools going on about the glory days of XP. It was little more than a warmed over Windows 2000 even at the time of release and people are all too quick to forget the massive teething pains that came with it. Suddenly users had to contend with user accounts, file permissions, a completely different driver model, IGPs of the day could barely handle the rather primitive skinning system. You look at the complaints people made about Vista and you'll see many of the same if you go back to around the time XP was released.
I recently had a home PC built specifically to tie into my home audio/video system. The goal was to have HDMI digital audio/video going out of the PC while being able to simultaneously broadcast two analog stereo signals to another source. This did not work on the initial setup therefore I had another sound card installed. Still not successful. I can only select one means of output to the multiple ports that I now have cables connected to. I am being told this is a Windows 7 issue and if I chose to go back to Windows XP I could make this happen. What is the solution?