It's possible to split the two Trigger Inputs on the TM-2. Doing so allows you to have two pads (or triggers) connected to each input, for total of four pads/triggers. To set this up correctly, you'll first need to get a "stereo insert" cable - like the Roland PCS-31L (sold separately), and then setup the Trigger parameters in the TM-2.
Note: You can also use any other similar stereo insert cable that you may have already. Roland also makes the RCC-5-TR28 as well.
https://www.roland.com/us/products/rcc-5-tr28/
Connections:
1. Connect the single stereo end of the insert cable (the end with the two black lines on it) to one of the trigger inputs on the back panel of the TM-2.
2. Connect the two opposite ends of the cable to each pad/trigger as shown in the image above.
Now that you've made the connections, we'll setup the TM-2's Trigger Inputs:
1. On the TM-2, press and hold the SHIFT button, and then press the INST button - "TRIGGER SETUP" appears in the display.
2. Press the + button (ENTER).
3. Press the 1 or 2 button to select the input that you want to setup.
4. Press + to choose PADx2" for the input setup. Choosing this setting allows the TM-2 to recognize the two pads that you have connected.
5. If you have pads connected to the other input, repeat Steps 3 and 4 for that input as well.
6. Press INST twice when you're finished. The new settings are saved automatically.
Tip: After you've made these connections and settings, be sure to follow the steps for "Setting the proper Trigger Type" available in this Knowledge Base for each of the pads. Doing so will insure efficient trigger results.