This is an old sample converter and digital selector for optical, SPDIF & AES formats. The sample frequency can be selected for 44.1kHz or 48kHz. Since this is old and you can get is as low as US$100 from ebay.
I use this to connect from my CD-PRO2 transport, SB3 or DAT as input and output to my D1V3, and other DAC or DAT. This make my switching among equipment more easy.
Here are the photos:
