The ART X-15 is a MIDI Foot Controller with two expression pedals on the left side and it complements the SGX-2000 in an excellent way. If you use these units together you can start right away using the expression pedals for many of the SGX's factory presets. It's also extremely easy to program the expression pedals that they modify arbitrary parameters of a preset. For a detailed product description of this unit please refer to the official product page for the X-15 MIDI Foot Controller, which is maintained by ART.

The look of the X-15 has changed analogous to the SGX-2000. In the beginning the unit has had the same colorful look as the SGX-2000. A picture of that edition is shown below:

When I got the foot controller serviced the first time the processor has been upgraded automatically for no costs. The upgrade was developed in order to enable users of the new SGX-2000 Express to access up to 200 presets with the X-15. Before that upgrade the X-15 was only able to access 128 presets. The new preset/bank model and the vast amount of factory presets of the SGX-2000 Express required this new version. The upgrade is not too expensive and a definite must if you have an SGX-2000 Express! Information on how to find out which software version your X-15 has and how to get the upgrade can be found at ART's homepage.

ART provides a PDF file of the English X-15 manual. Because of my general distrust in the availability of internet resources I made a copy of it. ;-)
Therefore you can download the Manual for the ART X-15 MIDI Foot Controller (1.1 MB) here. As far as I know there's no addendum available for an upgraded X-15 (i.e. one that can handle 200 presets rather than 128).

As a starting point I would recommend the official product pages maintained by ART at www.artproaudio.com. ;-)

A very useful page for the X-15 is maintained by Marcelo Garzón. Marcelo has written a Windows software that assists you in configuring your X-15 from your Windows PC. If you ever did some modifications on the X-15's configuration you know that it's not that convenient. You need to use the little display and strange button combinations to get what you want. It's impossible to do it without the manual next to you...
Marcelo's application comes with a graphical user interface and let's you setup your X-15 conveniently. Have I mentioned that it's for FREE? Download the X-15 Setup Program on his homepage.

Some hints and information about the X-15 can also be found at Vic Dyer's page. The page is called Musician's Users Group for the ART SGX-2000 Express and is mainly about the SGX-2000.

The most helpful reviews can be found at Harmony Central. Have a look at their section containing user reviews about the X-15.

• Very soon after I bought my X-15 I realized that the screws the expression pedals are mounted with loosen on a regular basis. There are at least two ways how to deal with this problem: one possibility is to have the proper spanner tool for the X-15 alway in your bag when practicing or performing. As soon as the screws loosen you can fix them again.
  The other solution would be to use a special paste that strengthens the fit of the screws more or less permanently. You can get such stuff in your local DIY superstore.