Diagnosing inadequate bass in an audio system.

For starters, check if speakers are wired in phase.  
Does the amp have plenty of power or just the bare minimum per the speaker manufacturer?

Are the speakers known for leanness/ fullness/neutral bass?

Speaker position.  Too far into room or far from room boundaries/ corners?

Oxidized speaker terminals/cables/interconnects?

Room too large?

Lean recordings/source?

This is a very broad question.  I'd say you need to be more specific. :)

Try this.