The Def Tech Pro 100s will give decent performance
in a smaller room but in an 18x20 they will be
inadequate. Speaker that size may be acceptable
for movie viewing if you have so so expectations
but try some budget small bookshelf speakers from
B&W, KEF, Monitor, Jamo, NHT, PSB, etc. doe 350/pr
+ a $250-300 center channel plus cheaper surrounds
and you will experience a sectacular improvement
over any sub/sat system. With some tough negotiating
you could pull it off for 1K. All of these sub/sat
systems are limited in their ability to move air
and you will notice it especially listening to
music. Bang for the buck, go with the Jamo's and
you could include a sub for under a grand.