3 possibilities :
1. The room was too small or difficult to analyse for the integrated microphone of the Beolab5, so that there were this lack of bass.
2. There was a material in the room, like wooden floor, that made the bass response misbehave, so that the Beolab 5 limited their bass level.
3. The beolab 5 were not calibrated correctly...
There is an interesting thread on the Beolab 5 bass issue on the general forum.
But what is sure is that the 5's doesn't need a Beolab 2.