How are the 70's set up right now, close to a wall, in a corner? How far are you sitting from them? did you run audyssey and enable dynamic eq? what is your source?
I know in my room my 70s produce enough low frequencies to impress me with music, though with a sub it is better. Even on movies I have been impressed. When I first got my 70s and was running only a stereo set up off my old denon 1611 the bass while watching inception on blu. was impressive, again not as good as a dedicated sub, but enough to wow me for a moment.
I don't need snobs to tell me how to think, thank you!