A receiver with HDMI standby passthrough can still send signals to your TV from connected sources like a Blu-ray player or game console, even when you don't want to power on the receiver and listen to surround sound.
A receiver's USB input gives you a quick, easy way to play the songs loaded on a USB thumb drive or your iPod (when compatible). Some receivers use the USB connection for firmware updates only, rather than for music.
Inputs and Outputs
An input that lets you connect any device with a coaxial digital output. Though coaxial digital connections use standard RCA-style jacks, a coaxial digital audio cable designed specifically for the wider frequency bandwidth of digital signals is recommended.
The total number of Component Video inputs. Instead of transferring video as a single signal through one cable (Composite Video), or as a single cable with luminance (brightness) and chrominance (color) separated (S-Video), Component Video uses three separate cables to transmit the luminance and two components of chrominance. The benefits -- improved color accuracy and less color bleeding -- are especially noticeable on larger-screen TVs.
An input that lets you connect any device with a standard optical digital output. Optical digital connections require a special type of fiber optic cable, known as Toslink. Since the signal is carried optically rather than electronically, an optical cable is virtually impervious to magnetic or electrical interference.