This looks like a great router. For the things you mention everything should work fine.
There are some things in a review that you don't mention as important, but may not be Mac compatible.
From trustedreviews:
"The RT-56U will also make any media files on attached drives available via a built-in uPnP server. We found this worked perfectly well with both a PS3 and an Xbox 360, with literally zero configuration required on our part, which is good. The RT-56U also has a software utility on a bundled CD that enables downloads over HTTP, FTP or BitTorrent to be handled by the router, with the files being saved to any attached USB hard drive. The only possible downside to this tool is that it is Windows-only."
So from this, I'm speculating and these may not be important to you:
If you want to use a hard drive attached, it will have to be formatted as FAT32 or NTFS, not Mac specific HFS+
To do bit torrent you need a PC or virtual Machine - I'd double check this, bc some routers allow you to control this through a web browser.
If I understand correctly? If you jailbreak your AppleTV 2, you could stream straight from hard drive connected to the router?
Also, I would advise setting up the apple TV 2 and steaming iTunes Mac on the 5GHZ N channel and let the other devices use the flexible 2.4 GHZ channel. IE if a wireless G device gets on the 2.4 channel, it slows every device to wireless G speeds until the wireless G device deactivates it's network connection.
My setup:
5ghz wireless N channel has the AppleTV 2, 2 Modern wireless N Macs, and 2 iPads that can use the 5GHZ channel.
2.4GHZ wireless b,g,n channel has two iPhones ( 1 G and 1 N) and three older Macs that have wireless G, only one of which is used daily.
This ensures that the older hardware does not slow down the AppleTV 2 or or newer equipment.
I hope this helps you or someone else
