A few comments based on my own experience.
Yes, you can make a really long ribbon cable to attach sensors to the SRX. When you do this though, if you're only using three conductors of the ten, you now have seven wires acting as antennas which can pick up noise and feed it back to the controller with potentially disastrous results. Ribbon cable is also very high gauge wire, and not made to be flexed back and forth. This can lead to breakage and if you don't have spare cables, a time consuming repair.
What we did last year for ours was to get some premade cables (so I know they are high quality and low chance of failure), and turn them into adapters for 3pin servo connectors. Here's an example from deep in the bowels of the robot:
http://i.imgur.com/vhGthdo.jpg (there was some tape holding the sensor wires on all season, no issues with the three pin friction interface)
This lets us have a standard connection design for all of our basic sensors so they can plug into the Rio or the SRXs. Our long runs are then just PWM cable, which is cheaper, easier to maintain, more robust, and higher gauge. You can also get the header and ribbon assemblies for free from Samtec as a sample request (part number FFSD-05-D-06.00-01-N)