John,
I think you are missing this part;
Yes the synth can play 16 channels with different instruments on each .. BUT if all of those 16 channels are assigned to the Default Synth, and you have an Audio Reverb plugin after it (due to the instance of the synth), all of them will have reverb.

The OP wants different effects for different 'Tracks', so these separate Tracks may need separate synth instances.

RB uses 'Ports' to send the signal to a certain Synth/Effect path.
If you want different effects for a given track it needs it's own 'Port' assignment (new instance of the synth with different AUDIO FX after it) so the FX only affect that Track.

Example:
If Tracks 1-8 are all assigned to a given Port (say the Default synth Port), then putting an Audio Reverb effect after the synth, say in slot 2-4, will affect all the other Tracks using that default Port. This can either save resources or be a hindrance.

To make a given track different, it needs to have its own Port (or path) so the Audio FX that follow that synth instance (or Port) are handled differently.

I suppose a drawing would help (and I think I've posted this before), but the flow is:

Track goes to Port (1 thru 32)
Port assigns synth (hardware or software) if MIDI.
Or it can select the Audio Out Port, if an Audio Track.

Audio FX follow the synth assigned to the selected Port (if a softsynth/MIDI track).

So selecting a different Port, then assigning a new instance of the desired synth to the new Port creates a new 'path' .. and then you can assign different Audio FX to that path (after that instance of the synth of course) to make them different.

I'll see if I can clarify with images if needed.

I do not work here, but the benefits are still awesome
Make your sound your own!