I've been through similar issues before with legacy hardware on newer operating systems. The CMI8738 is a common challenge but there are a few routes you can take. First, it might be worth checking some tech forums or websites like DriverGuide, as community members sometimes upload working versions of hard-to-find drivers. Also, consider trying compatibility mode: if you find any older drivers (perhaps for Vista), install them by right-clicking and selecting "Troubleshoot compatibility" to see if Windows 7 can adapt them.
If you encounter persistent issues, another option might be looking into generic drivers that support a range of C-Media chips. These might not unlock all features, but they could get basic sound functionality working. Lastly, while it's always ideal to use existing hardware, sometimes a low-cost USB sound card can be a quick fix if you need sound urgently. Let me know if you find something that works!