Sure! If your TV is connected via its Audio Out to your 321's Audio In, anything that can be connected to your TV will make it to your 321. An AppleTV's HDMI connected to your TV will play fine, with solid audio pass-through to your 321.
Before streaming video, we used a Motorola Bluetooth adapter connected to the 321's AUX via RCA (red & white) to play music from computers, iPods, and such.
The 321 is only as 'smart' as what's connected to it - after that, you've got it made.