Shows the basic routing. Notice how Split mode splits the oscillator inputs to each filter. This can wield some really dynamic results when modulated independently. It's almost like having two different patches. Split filter mode is also unique in that it pans each filter to either extremes.
The Filter Balance knob (all filter modes) controls the input and outputs of each filter. Turned fully anti-clockwise the signal (oscillators) will be routed just through Filter 1 (as if Filter 2 is bypassed). Turned fully clockwise the signal will be routed to just Filter 2 (as if Filter 1 is bypassed). In the middle, it runs the signal through both Filter 1 and 2 together as per the given configuration shown in the routing diagram for any particular routing mode.
The above can be a bit complex to get your head around as Filter Balance's mixing control is actually multi-faceted (three pronged) - in that, depending on any selected value for Filter Balance, the routing is changed further still. I'm going to redo the above picture to take filter balance into account, as the explanation in the (Virus B) manual is poor (not sure what the TI manual is like) and I feel it's a key element to grasp properly if you want to fully understand how the filter routing works.
If that isn't complex enough, also bear in mind that the Filter 1 cutoff value also modulates the Filter 2 cutoff value when Cutoff Link is enabled. Enabled or disabled gives very different results, as it directly affects how the filters interact with each other. When enabled, Filter Cutoff 2 acts in a completely different way, sympathising with whatever value Cutoff 1 uses, as opposed to working independently when disabled.
As you can see, it's very easy to lose track! At first glance the small number of filter controls belie the flexibility and complexity of the results that are possible.