New to HT. please be kind. Thanks

What should i purchase first? Should i purchase a good reciever first or shall i purchase The M40ti first? My current reciever is just a Dolby Surround Pro Logic with NO optical inputs/outputs. so exactly what does that mean? I thought i had to have optical input for it to decode and seperate all the sounds to different speaker if i'm watching a movie on a dvd player? How does it do this when the Inputs into the Receiver are just by a pair of L/R RCA wires? i'm confused. Thanks