The KeyStep Pro does not send midi CC, after touch, or program change messages out of the midi out. If you have external gear hooked up to this port, you won't be able to do the above mentioned. By setting the second midi out to a thru however, all midi information will now be passed through to external synths, meaning you can now send midi cc, after touch and program change messages, etc and have your external gear respond, which was not the case before.