I would read through the section of the manual explaining the onboard switches and how they can be used also the section I cut and pasted below. Also the FAQ link below has some info on Aux Switches. Any momentary switch will work with a TRS cable. There are 3 switch units out there. Boss\Roland makes different styles.
From the manual…
“The rear panel Aux Switch stereo phone jack supports up to three independent momentary switches using Tip, Ring and Tip+Ring. Aux Switches do not disable TimeFactor’s Footswitches – the local Footswitches are always active. Aux Switches can be programmed to perform a number of functions and they make it easy to connect a dedicated Tap Tempo switch or Repeat switch or Preset Switch.
As noted above, the TimeFactor has two operating modes, Bank and Play. An Aux Switch can be used to instantly toggle between the TimeFactor’s Bank and Play Modes. Alternately, some users may want to have all six switch functions immediately available (3 from each Footswitch Mode). A set of three Aux Switches can be connected and assigned accordingly.
Aux Switches can also be assigned to parameter values allowing you to switch between two parameter values. For example, you could assign an Aux Switch to change Delay A’s feedback level (Fdbk A) from 0 feedback when the switch isn’t pressed to 100% when it is pressed. To program the Aux Switches see the System Mode section of this User Guide.
1) You must use a stereo phone 1⁄4” plug to connect Aux Switches.
2) Toggle switches are not supported. Only momentary switches will work properly.
3) Simultaneously pressing the switch assigned to the Tip and the switch assigned to the Ring will trigger the function assigned to the Tip+Ring. The Aux Switches should be pressed independently.”