ARC = audio return channel
If you're using the tuner on the TV for cable, you don't have to run an optical cable from the TV to the receiver for the sound, it will go "backwards" on the HDMI cable that normally carries the video signal from the receiver to the TV.
your TV and receiver have to support it, not all do.
not all TVs will send audio that comes in over HDMI out over the optical port or the ARC, so read the manual carefully before purchasing if that's what you want to do.
if you only have 2 HDMI inputs, and have more HDMI sources than that, you'll need an
HDMI switch that has multiple inputs (2 to 8 on the page i linked) and 1 output. you can then switch between those inputs, normally using a separate remote control, or sometimes a manual switch.
or...
if your TV and stereo suport ARC, and your TV has enough inputs, you might be able to get away with plugging the extra devices into the TV, and using the TV in the place of the switch i mentioned earlier.