Band in a Box can, by design, generally access only one midi port at a time. However there are some ways to make BiaB access multiple ports if needed.
Hardware Synth + Hardware Ports
If you are using a hardware synth, such as the Ketron SD2, and wish to send midi data to another device with a separate hardware port (no soft synth) you can use Midi Ox/Midi Yoke.
Install Midi Yoke according to the software directions. The install program will, by default, put eight additional midi ports on your system. These are named 'Midi Yoke xx' where xx are sequential integers.
Install Midi Ox according to the software directions. When done, launch Midi Ox and connect the first Midi Yoke port to your hardware synth. Then connect the same Midi Yoke port to your additional hardware device. See Figure 1.
Inside BiaB choose the first Midi Yoke port as your midi output and make sure the 'Use DXi/VST' checkbox is unchecked. When you play BiaB the midi output will go to the Midi Yoke port where Midi Ox will redirect it to both hardware ports.
You will most likely want to filter the data in Midi Ox, or in your hardware devices, so that only the relevent channels go to the correct ports. That will depend on the hardware you are driving so it's not possible to guide you here. You'll need to read the documentation of your midi devices to determine what data should go where.
Software Synth + Hardware Ports
If you are using a software synth, such as the Coyote Wavetable, and wish to send midi data to a hardware port as well you have a number of choices depending on what data you want to send to what Midi Device.
Controler to Hardware Device
For example, suppose you want to send data from your controler to a vocal harmonizer or midi lights so you can send data by keystroke.
The first method is to open the Midi/Audio Setup dialog from the main menu. Select the relevent output port and check the Send midi thru to midi port option. Anything you play on your controller should go to your output port and thus to your hardware device(s).
On some systems this has been reported to not work. In that case you could put the MidiRedirector on the Thru track and select the hardware port of interest. This should send your midi data to the output and hardware device(s). You must pay attention to channel selection within your controller and hardware devices.
Chords to Hardware Device
BiaB can output chords to a midi device such as a vocal harmonizer/processor. While using a software synth like the Coyote Wavetable (Use VST/DXi Synth box checked in Opt|Midi/Audio Setup) the chord output does not go to your selected midi output port (as of BiaB 2013). You must first set the output channel in Prefs|OutputCh to be the same as a blank track. If you aren't using it, the Thru track is the best selection. The Thru track has a channel number of 5 in a default setup.
Next, insert the MidiRedirector plugin on the Thru track. In the plug, set the output port to the appropriate selection. Set the force midi to channel option to the correct channel for your hardware device. Now, when you play BiaB, the chord data will be output on the Thru track, changed to the correct channel and redirected to the hardware device.
Melody to Hardware Device
If you wish to send melody (or another track) data to a hardware device, while 'Use VST/DXi Synth' is checked, BiaB has no internal way to accomplish this. However, there is a way you can do it. The exact procedure will depend on whether you have a hardware synth available or whether you rely entirely on software for your midi sounds.
First, if you have a hardware synth available, and it is daisy chained to your additional device, then you can use a one step procedure. Put a copy of MidiRedirector on the melody (or other) track you wish to send to your hardware device. Choose the port which has your device(s) connected. Now, when you play BiaB, the melody will go to your hardware device and synth. You may have to filter channels at your devices to make everything work correctly. For that you'll need to refer to your hardwae manuals.
If you have a hardware synth and it is on a separate port you will need to use Midi Ox/Midi Yoke to send data from one virtual port, using MidiRedirector, to your two hardware ports (see first section above).
Finally, if you have no hardware synth but still wish to hear the melody you will have to duplicate the melody data on a blank track using the BiaB menu commands Copy/Move Tracks. With a duplicate melody track you can use MidiRedirector to send midi data from the duplicate to your hardware device while listening to the original through your soft synth.