While many receivers offer much less power than they are rated, the Ventriloquist is designed to work well with low power so there is not much of a problem there. The quality of electronics has improved recently, and Dudley is right... there isn't much source material that uses all the channels at once.
No harm will be done with seperates. However, my opinion is that good room treatment (Sonex) and good subwoofer placement will make a more noticable difference than seperates will. A little Sonex to absorb first order reflections can really improve the highs with any speakers.