Still come from the RCA/Phonos if i plug a set of headphones into a '3.5mm Jack Socket to RCA/Phonos and plug into my TV. The reason being i've just bought a pair of headphones and wondered if it will work with my Xbox's audio even if its HDMI?

let me put it like this     
 
Headphones(3.5mm Jack)-------------->3.5mm  socket to RCA------------->TV 
Xbox----------->HDMI------------>TV 
 
Will audio come from the former if the bottom exists?.

Yeah, it'll totally work.

YES!!!! thankyou!! wasn't sure if it would work .

sure will, you can also use HDMI for video and the optical out for your audio if so desire, like i do so i can use my wireless head phones.

@Kandycane2029 said:

Yeah, it'll totally work.

will sound quality be lowered through doing this? 

Not sure about that, but I don't notice too much of a difference when I'm using headphones through my TV.

Edit: You could also look into getting one of theseas they're pretty cheap now.