Hooking up an external blu-ray player to a home theatre system with a dvd player

I have a home theatre system with a 5 DVD player built in...but it's not blu-ray.. SO, now i have a blu-ray player to hook up to that..... I want the surround sound etc to come through when we play a blu-ray dvd but right now, i'm not sure how to do that... IF I connect the blu-ray to the main receiver/dvd player via an HDMI cable..... what would I select on the home theatre system to play the blu-ray disc. Right now i have the blu-ray hooked to the tv using Input 3..but that's only player to tv...(which is connected to the home theatre....) BUT only the tv speakers output... IF i connect the blu-ray to the home theatre via HDMI.... and select DVD/CD etc on the home theatre option...will it somehow read that it's a dvd from the connected blu-ray and NOT one within the actual home theatre player?????
clear as mud I'm sure.. .
thanks!!