I don't think it matters if you have 2Box module connected with USB, module is not in USB mode anyway. Well, here are three pictures that show my setup. My midi interface is m-audio midiman.
1. First you enable MIDI device

2. Then you add a track and select input. I selected all channels as I only record one midi at a time. My 2Box module is setup to Channel 1 (UNIT-INTF) meaning I have to select either channel 1 or all channels.

3. You arm the track and start recording. No picture here. That button next to I/O on track must be RED.
4. To playback and record you must setup MIDI output. Click I/O to open routing window and select your MIDI interface that will send signal to 2Box module.

5. Add new track, select input from your soundcard, connect outputs from 2Box module to your soundcard inputs, configure 2Box module to send drum sound to whatever output you wish (ie. 3+4) and record. Don't forget to disarm MIDI track. Reaper will send signal to 2Box module through MIDI interface and record sound (wave) to this new track captured from 2Box module. You can also record directly to your mp3 recorder if you connect 2Box outputs directly to mp3 player.