Why iTunes? Why not iPhoto, or the Movies Folder?

Question

I hope this does not come across as just ranting. I think I have a couple of intelligent questions here, and am genuinely confused.
I'm far from new to the Mac. But admittedly have stalled as Apple moved toward mobility and sharing. I do not have any iOS devices; stopped upgrading at Snow Leopard; was sad to see my .Mac become .me, and now evaporate into a cloud. I am not really doing much with iCloud, other than the bare minimal to keep my many years old .Mac email address. I do, however, have and use a Mac Pro, two MacBook Pros, and some older Powerbooks and iPods.
And now, I have an Apple TV. I just got a new ATV (Amazon listing said "newest" so is that gen 2 or 3?).
Weather 2nd or 3rd gen ATV, I am having a difficult time using it to play so much of the content I have on several different internal and external hard drives.
I falsely assumed that video I created or edited using QTPro or iMovie would have an easy and logical route to the Apple TV.
Wouldn't it make sense to stream from iPhoto, which has video uploaded from digital cameras, or anything in the User Movies folder?
Any video I have on non-boot drives, internal or external, has no simple way to be played on the ATV.
For years, working with video, It did not make any sense for me to use iTunes. Hence, the greater percentage of my stuff is not mp4 or m4v, though I try to use H264 now as much as possible. Still, I have much in avi; divx, wmv, mkv, etc. For that reason, I have 2 Sony Pplaystations (PS3) for streaming to HD TVs. But those do not like Apple proprietary video. Which is why I broke down and bought the ATV.
I am accustomed to having to convert things and have several good video conversions applications, as well as QTPro.
But the video file type is not my main issue right now. I knew the ATV would not play all those other file types.
What I did not know, and am struggling with now, is the fact that everything has to come from iTunes, which resides on my boot drive, which only has a fraction of the movies and tv shows I want to stream to the ATV.
So...Do I have to create multiple iTunes Libraries and store one on each of the non-boot drives?
If so, how do I use the ATV to select the Library I want to use?
I do have Home Sharing turned on. As I mentioned, I do not use or have any iOS devices, only multiple laptops and desktops and older iPods.
So Airplay, as I understand it, is not part of my scenario?
Nor is syncing, since this is a ATV 2 or 3, right?
I did figured out one clumsy method of getting video from other than iTunes, but it's limited. It's this:
In iTunes, I go to Advanced > Choose Photos to Share. Then in the Photo Sharing Preferences box that comes up, next to Share Photos From: I select a folder on one of the non-boot drives, and check the Include videos box. It works, so far. But as best I can figure, I can only make one selection (folder) at a time.
Help, advise, comments will be much appreciated. Thanks

Answer 1

The requirements for AppleTV were clear to me that iTunes is required to play videos. Also the video formats were listed in the requirments.
You have to have iTunes running to stream the videos to your appleTV, but the iTunes library does not have to be on an internal drive. My iTunes library is on a 2TB external drive. I know others have multiple external drives making up their iTunes library but I do not know how they accomplished that.