I would just like to update this thread with the results and solution of the issue I was experiencing when trying to stream PCSX2 through Steam In-Home streaming.
As suspected the issue was indeed caused by having multiple windows open in PCSX2 that Steam was then trying to stream all of the windows to the Client PC. Apparently Steam gives priority to the first window opened and then any subsequent windows are given way less priority and will chug badly on FPS as a result. So the solution is simple, you just need to eliminate the extra windows and make PCSX2 launch the ISO game file directly to the GSDX game window. As Blyss Sarania posted earlier in this thread, that is very easy to do by adding the following after the Target File Location of your Shortcut for the game in Steam:
--fullscreen --nogui "C:\directory\name of game.iso"
And that's it. Launching the game via that customized shortcut will launch your game's ISO file directly into the GSDX window without the Main GUI. Just be sure you have already disabled the Console Window within PCSX2 prior as well. Steam should stream the GSDX game window by itself just like any other games you may have streamed previously.
I'm now rocking a solid 60 FPS streaming to my living room TV while playing FFXII in full 1080p glory with full anti-aliasing and antistropic filtering. And my god does it look good! My poor PS2 is sitting right next to the TV being all jealous that my PC is doing a much better job than it ever could, making it obsolete, haha.
Thanks again to everyone for your help and information. I'm so excited to be playing this game in all it's proper glory now!
<3