Not for nothing - but - "......Adding magenta to a yellow, only cancels part of one out. say you have a 65 yellow and want to add 20 magenta. What you are effectively getting is a 45 yellow. It will not effect the density at all. just dial in the 45 yellow......."
is not completely true. Most multi-garde papers are now made up of two emulsion layers, and as stated, each activated by one of the above filters. Mixing these will produce a contrast (if not density) different from using only one or the other. Another example is the design behind most VC cold light heads where two bulbs change intensity of mixed color as you shift contrast.
With that said- David - Why not teach yourself the difference with the; paper, enlarger, etc. you are using by running comparitive test strips. Seeing the difference will help you understand the materials response to these changes.