Depends on one's exact design approach - what they are housing. It could be something like this with a specially optimized input board, but not significantly less:
https://ghentaudio.com/kit/ncore-se-200w.html
Otherwise, with a shared power supply, like that used by Purifi for their demo build, it can be made to fit in that size case with existing parts, as shown here in a mock-up with a Purifi EVAL1 I/O board (or other available I/O boards):
https://ghentaudio.com/kit/ncore-se-200w.html
Otherwise, with a shared power supply, like that used by Purifi for their demo build, it can be made to fit in that size case with existing parts, as shown here in a mock-up with a Purifi EVAL1 I/O board (or other available I/O boards):