Connect the DM6 USB directly to your computer for MIDI. And the audio from the DM6 to your audio interface.
Please read this article for setting up External MIDI Devices with Studio One 3:
http://support.presonus.com/hc/en-us/articles/115001352966-Studio-One-3-How-do-I-setup-a-hardware-keyboard-synthesizer-in-Studio-One-3-
To use the sounds of your DM6 and sync it to Studio One;
1. In Studio One External Devices window, you will need to create a New Instrument with the MIDI "Send To" set to your DM6s MIDI port. This allows the sending of MIDI+sync from Studio One to your DM6. The DM6 has to be set to external MIDI clock.
2. To use the drum pads to record into Studio One, you will need to create a New Keyboard, with the MIDI "Receive From" assigned to the MIDI in of your DM6 port, but don't need the MIDI "Send To." And set this to Default Instrument Input.
3. Connect audio cables from your DM6 to your audio interface so you can monitor the drums in Studio One.
Then, check out this article on setting up to record using an External MIDI Device: Setting up to record with an External MIDI Device Studio One: http://support.presonus.com/hc/en-us/articles/115001418283-Setting-up-a-Song-to-Record-With-External-MIDI-Devices
Please create a support ticket if you would like to discuss this in more detail.
Here is a link to create a ticket: http://support.presonus.com/hc/en-us/requests/new
