I’d like the red & white audio RCA plugs from a video game player (Gamecube actually) to receive the 3.5mm plug to my headphones, bypassing the stereo/TV/DVR etc. I could route the audio through a stereo or something but don’t want to at the moment.
So, I found this 2 x RCA Female / 1 x 3.5mm Stereo Female Adapter.
My question: will this work? Obviously the connections seem right, but will the sound be okay, or does the audio from the video game console need to be amplified or otherwise somehow “handled” by a receiver or something, before outputting to headphones?
The output from your game cube is at a fixed line level. You will almost certainly need some means of amplification and a way to control the volume with this arrangement.
Pitter Patter is correct. The Game Cube spits out audio at line-level and you need it amplified to headphone-level. You can use a component as you mentioned. You can also google “headphone amp” to see some dedicated products.
One popular DIY project is CMoy.
Well, I found an old component switcher (unpowered) with four inputs and two outputs. The second output wasn’t labeled headphones, but looked like a 3.5mm headphone jack. I tried putting the GC through the switcher and plugged headphones in. The audio was fine through the left, but static-y & low through the right. I’ll have to play around more with it though because I started having the same problem with other audio devices too. I think I really should power everything off before switching cables around.
Anyway, the sound was okay, and I don’t think the switch amplifies anything. Plus, some video games do allow you to adjust game, FX, etc. volume levels through the GC. But, you’re right of course there’s not a lot of audio control.
I don’t want to order that little adapter and pay $6 shipping for a $1.63 part but I couldn’t find it available at Radio Shack (online). Next time I’m at my local one I’ll see if they have the adapter and if it’s cheap, I’ll try this experiment anyway.
Anyhoo, I’ll dig out the stereo receiver and use that. I just didn’t want to use a 100W stereo to run a pair of earphones. 
I used to use a “passive preamp” with my computer for headphones. That might be a good Google (ebay?) keyword for you.
You can throw one together with a stereo headphone jack, an RCA jack, and a stereo potentiometer. I stole all of those components out of an old CD player.
Now I have a headphone amp similar to the CMOY one linked above. It’s built into an Altoids tin