You would keep your sorcerer and bard spells separate from each other. Your total number of spells per location is a level 6 launcher, but your known spells are separate. To help explain things a little better, let me explain more in depth.
As a wizard, you know 4 traps and two first-level spells.
As a bard, you know 3 traps and 8 spells that can be third, second or first level spells.
Since you have two multiclass spell casting classes, you can cast 4 first level spell locations, 3 second spell locations, and 3 third level spell locations.
You can choose that these spell locations belong to one or the other class and can even boost certain spells. For example, a magic missile can be cast as a third-level spell even though you only have a magic missile in your wizard class.
TLDR: It can only take new bard spells in the bard spell list.