ATOM only works in Studio One V4 onwards. That is natively though. Not sure how you could get it to show up in V2. What OS are you on and version of OS.

Windows 8.1. I added it to where it was registering when I hit the pads, but it just wouldn't seem to trigger any Impact or any VST instruments.

You have created an Instrument in your External Devices which is something that receives data from Studio One, not sends it.

But leave that for the moment. Although edit this and you should only have SEND TO connected to the ATOM. RECEIVE FROM should be set to none. ATOM does need to receive data in order to display certain things correctly though.

Now add a keyboard to your external devices. Set the RECEIVE FROM to the ATOM and SEND TO to none.

For each device (that needs two way communication) you need two things. A keyboard (Sending) and an Instrument (Receiving)

Your MAudio 61ES is setup correctly as it is sending into Studio One. Basically ATOM is alao a keyboard because it is sending.

Now when you create an Instrument track in Studio One, you can set ATOM as the input source and it should trigger whatever virtual Instrument you have that track pointing to. eg Impact

I added the ATOM as a keyboard but I can't get it to connect. Is it supposed to have the checkbox under "In" like the 61es? Also, ATOM pads trigger the keys in MIDI learn mode even those it shows "Not connected" in the External Devices Options.

Its been a long time since I have used V2.5. Actually I have got it still setup on one of my old computers and I will do a little check for you. How did you install the driver for ATOM for Studio One V2. When I connect it to an older computer it is asking for the driver to be installed.

I have only got Studio One V2.6 installed on an XP 32 bit machine so I doubt I will be able to get it connected.

When it says it is Not Connected in External Devices it generally means that device is not available. It is interesting that the pads are triggering in Learn Mode though.