Assuming you are talking about the USB cable between your Audio 6 and your Mac? Yes, you will still need that to get the audio to and from your Audio 6 and your Mac and then into Logic for example..
The cables you are buying, are just to get audio to and from your Audio 6 and your FX Units.... not the Mac... The USB cable handles all audio signals between the Audio 6 and your Mac.
Please note: Due to the limitations of your Audio 6 (which only has four physical audio inputs/outputs...) you may only be able to connect one of your FX units at a time.. (depending on what you use the other inputs on your Audio 6 for.. like a mic , guitar or external Synth..) unless you chain them together... as in..
FX unit #1 Outputs to FX Unit #2 Inputs... then FX Unit #2 Outputs to Inputs on Audio 6... then... Outputs on Audio 6 to Inputs on FX Unit #2 and Outputs on FX Unit #2 to Inputs on FX Unit 1
You will need extra cables to achieve this... such as 3.5 mono to 3.5 mono cables to connect the FX Units together...
Bear in mind the audio signal will then flow through both FX Units...so you must decide which order to place them in the chain to get the desired workflow you wish...
Hope this makes sense... It probably will make more sense once you wire everything up and play with it all 🙂
Nigel