You have it right so far. In Devices, select an unused device slot on the left. Set Manufacturer to Generic, set the name to DPC (or whatever you want). Set the MIDI Channel to a channel you're not using for any other of your devices.
Now, we need to assign a button temporarily to do what the device requires to set its MIDI channel. Go to the Buttons tab. Double click a button to open it up. Set Button Type to IA. Turn off all checkboxes. If there's an action in the action list (gray box, bottom left corner), select it. If there's nothing in there, press Add Action.
Now, in the bottom right, set Action Type to CC Toggle and Device to DPC. Set CC Number to 99. Off Value should be 0 and On Value 127. Click Done to finish. Send the settings to your PBC.
Now, power up the DPC while holding the 1 button. When it powers up, press the button on the PBC that you just edited. That should assign the MIDI channel on the DPC.
Now, select an unused button page in the Buttons tab. Start editing the buttons as you did before, but with these settings:
Set Button Type to IA. Turn off all checkboxes, except Send on Preset Change and Update on Preset Change, which should be turned on. Set Action Type to CC Toggle and Device to DPC. Set CC Number to 50. Off Value should be 0 and On Value 127.
The above will set up a button for Loop 1. For Loop 2, do the same but use CC number 51. Use one higher number for each subsequent loop button.
Now, you need to have a way to get from the main button page to the new page. On Page 1, edit the Function button (bottom right). Turn off all checkboxes, except turn on Momentary. Edit the action on the button to be type System, subtype Page. Set the page number to the page that you just created. Click Done.
One more step - click on the button you just edited, and in the Edit menu, select Copy. Now, switch to your new button page, click on an unused button, and in the Edit Menu, select Paste. Double click the button to edit it. Change the page number in the bottom right to page 1. This button will be what you use to return to the new button oage.
Now, send the settings back to the PBC and you can test it - the buttons should control the loops on the DPC