Hi
The Basestation Pro currently has several sockets on the back that do not yet do anything. These are, as Geert has pointed our, a MIDI in/out pair, an extension socket with the same connector as the instrument and an I2C port with a latching mini XLR connector.
We will be implementing these over the next few months, starting with the extension port. The firmware for this is now complete and is in testing, so you may see a firmware upgrade become available that enables this in the next few weeks. This port allows you to extend your Basestation Pro by connecting it to a Basestation (the one that currently ships with the Tau) using an Eigenharp cable. The Basestation Pro, Basestation and the Eigenharp can then be powered from the remote Basestation. This means that you can have the Basestation at the back of the stage, next to your computer, while the Basestation Pro can be out front where you're playing so that your pedals are where you need them. Also, if you're playing in a situation where there may be moisture present (such as an open air stage) the interconnect only carries 24V, so performer safety is improved (although we seriously advise that you do not get your Eigenharp wet, they are not designed to deal with this). If you currently own a Basestation Pro you will need to add a Basestation and an additional cable to be able to use this feature. If you own a Basestation you will need to add a Basestation Pro and a cable. Both the Basestation and Basestation Pro will become available as accessories shortly, probably to coincide with the firmware update.
The MIDI in/out ports are a work in progress at the moment (firmware mostly done, host software not started as yet) and it is likely that they will be enabled in a firmware update later this summer, probably at the same time as improvements to the way that MIDI is transported within EigenD. We are planning that these will be general purpose MIDI I/O, although they are mainly intended to be used with footboards and pedals.
The I2C port is currently planned to support additional accessories. We have early plans for an extender box to be able to use more continuous control pedals as I think two is a bit light. There is no ETA for this. We're also adding this port to the Basestation later this year so that any accessories that can be used with the Basestation Pro can also be used with the Basestation.
I hope that clarifies things..
John