Like I said, you like your 2 channel system, why change it??
just add a digital AV pre/pro (looped into an auxilary input on your existing 2 channel preamp(switch to that input for movies), and a subwoofer. You will keep the integrity of your 2 channel you like intact, and have added the HT part...simple really.
If you start over, you'll have a more difficult time "getting it all right" starting over. Plus, more complication, diffuculty in placing all the other speakers for good sound(even,matched sound, and balanced). You'll, in the end, just have "more speakers", not necessarily better.
Of course, I'm not sure what your speakers can do for movies. Some audiphile speakers are "too laid back" and uninvolving for movies. They don't jump out and grab you, but rather make you lean into the movie, and are distant sounding, not upfront and pressent!...this is critical for an effective movie mix...I don't care what any audiophile say's...it's booooooooring. (been there, done those...)
Still, I'D CHANGE ONLY ONE VARIABLE AT A TIME!!! This is the right way to do things. You go changing too many things at once and you don't know what you've got going!!!...or where the problems are.
good luck