The C603 does have a better and stronger bass response than the C403.
I know this because I have heard both off them, in the same system.
But I have no idea if it will satisfy your own personal bass needs.
What kind of music do you listen to? What are you using as a source for the music?
How will you be setting them up (placement)? On bookshelf speaker stands?
On your desk? Other?
They are a rear ported design, so they do deliver their best bass roughly 18 to 24 inches off the backwall. If you place them up against a backwall or only a few inches from the backwall; you will be disappointed in the bass response.
How far from the sidewalls will each C603 be placed?
How far from the speakers is your sitting/listening position?
The C603 won't have a problem cranking in a 14' X 14' room. I know this because I had them in a very similar 15' X 15' room and they sounded great.
I don't know much about your receiver, so I have no idea how the C603 will mate with it. But they are a 6 ohm speaker and they do drop down to 3 ohm and hang around the 4 ohm area when there's deep bass. They like good quality power. They responded wonderfully to seperate amplifiers, too.
A quality receiver withn a quality power supply.......should have no problem driving them and pumping excellent bass.
How you define excellent bass, is another story in itself.
In other words, your guess is as good as mine

