I am going to DIY my PC case. But this problem happens to stock cases also.
For example, I use the Gigabyte GA-Z97X-UD5H-BK motherboard. It has 2x USB 3.0 and 4x USB 2.0 ports through the internal USB header. If my PC case has less than (2+4) USB ports on the front, the capability of the motherboard is not utilised.
One solution is to add a 5.25" Drive Bay with USB ports. I would need (at least) 2x USB 3.0, 4x USB 2.0, Audio In, and Audio Out ports. It is not easy to find a product that fits. Are there any recommendations from high quality brand?
More importantly, I would like a more customise approach. Can I buy some dangling USB ports (as well as audio in/out ports) and fit them into the cut holes of my PC case? What exactly the terms of those products that I should search for?