He has been tracking and reporting on CM4 host board developments.
The MirkoPC is a fairly well balanced host providing mini PC capabilities, designed by a one man team in Poland, doing a job on par with some pro manufacturers.
The MirkoPC has 32-bit/384 kHz stereo line out using a hifiberry-dac driver. It also has a PCIe x1 (single lane) socket that accommodates PCIe x1 drives.
Geerling’s tests find the initial 7 seconds boot time is much the same for NVME drives and SD cards, while application load times with NVMe storage is 44% faster than microSD
A commercially available minimal host board for those who just have to try a compute module, that’s the size of a standard Pi, (with fewer USB connectors) but sufficient to built a Zynythian, is available from Waveshare (the display people) for $36.99.
They also have a more elaborate board for $10 more with more connectors and power over Eithernet.
There’s also a single purpose high fidelity audio output box with multiple connections, the Mercury Streamer which accommodates the CM4.
It might fit into a pro studio but is not the makings of a Zynthinan. This furure product seems to have the same capability of their Pro Audio Shield for the Pi 4 , the Pi2AES available for order now. ( 4-6 week lead time, requires a 24V power supply)