The computer I selected for this project was the Domino.IO Core, mainly because it shipped very quickly and was readily available. This computer was short-listed because it has a very small form-factor and low power usage making it great for portable battery powered operation. It also has built-in Wi-Fi, so there's no need for additional modules as well as I2S for transmitting digital audio signals. Another added benefit is that the boards it can be mounted on are open hardware. Unfortunately the computer itself is not open source. However, it may be replaced with any other Linux based Single-Board Computer with very little change in design.
The DAC selected was the PCM1754DBQ. It has a high sampling rate (up to 192 kSPS) and a sufficiently high bit-rate (24 bit) for high quality audio reproduction. It can also be directly connected to the SBC through I2S.
For the audio switching, the ADG736 SPDT audio switch was chosen because it has a low resistance and is able to switch bi-directional current (essential for switching analog signals).
Finally, I decided to go with a CMoy amplifier design. It's a very compact and easy design to implement, and there's tons of resources available to design it, such as the tangentsoft website. This website provides all the information required to build the amplifier and ensure it's running correctly, making the design ideal for getting the project up and running. This may be easily replaced with a more advanced amplifier at a later date. I decided to use the Burr-Brown OPA2132PA op-amp to implement this amplifier, but there's a wide selection available with their own unique sounds and features.
While researching amplifier circuits, I came across an awesome CMoy amplifier using P2P wiring. Given that I don't really have access to any PCB manufacturing equipment and I want to limit the cost of the build, I decided to use some P2P wiring myself. Also I reckon it looks pretty cool.