What do I need?

A home theater requires a surround processor AVP)… which takes input signals from different sources like BluRay, Cable box, Amazon Cube, Apple TV and splits them into different channels (basically a multichannel preamp and decoder). This signal is then fed into a multichannel amp. There are also AVP that contain seven or more channel amplifiers. Most folks (non-fanatic) use these. They do not sound as good as audio only components, but since video distracts you the sound quality is not as critical.

i have separate AV and audio systems (preferred). My home theater has a surround processor and a separate five channel amp. You can see my systems under my user ID in virtual systems.

What is your amp and preamp?  Does your preamp have a home theater pass-through?  A pass-through will take the front two channels from a surround processor and deliver it to your two channel amp without affecting the signal (the volume is controlled by the surround processor/receiver).  I do this by using a Onkyo receiver as a surround processor (my preamp has a home theater input).  The Onkyo also has amplifiers for the center and rears, but I'm sending those channels to separate amps.

@tochsii You can power a home theater with 2 channels just fine. You will not get any surround functions, but you can't miss what you never had. 

If you’re gonna now have additional speakers for HT the cheapest/easiest thing would be to get an A/V receiver with front L/R pre outs that you can feed to your stereo preamp and power the other speakers.  If your stereo pre doesn’t have a HT bypass this can still work very easily using any unused line level input on the preamp, which I can elaborate on if needed.