I used this DAC with an old Raspberry PI-1B I had lying around. I'm very pleased with the resulting sound (pioneer amp and 80s-era KEF speakers).
Unlike later RPI models, the necessary I2S connections to the RPI-1B (Version 2) are made not via its 26 GPIO pins. Where to make the connections is very clear from he DAC documentation/schematic (on the audiophonics website). Rather than soldering wires directly to the RPI PCB, I soldered a "2.54mm Separable Male Pin Header 2x4 Pins 5.5mm (Unit)" to the RPI and connected this to the DAC using "I2S 2.54mm Female / Female Cable 1 Pole Silicone 17cm (x5)". All really easy.