There is one thing I have discovered something related to the Covox a few weeks ago that I have not seen been mentioned in this thread.
Have any of you heard of the Intersound MDO? Apparently it was a parallel port soundcard similar to the covox. The CVX4 and other covox clones are compatible with games that supported this Intersound MDO card. They all come from the same developer, Coktel Vision.
Here is a incomplete list of games that support MDO:
Why do I say incomplete? Well I found out there are more games from the same developer that also support the soundcard.
For example the demo version of the first Gobliiins game supports it. Here is the demo:
Go.bat is the loader to change sound card settings
Also this game called A.G.E. supports the intersound MDO, but does not have any soundcard info on mobygames:
There might be more Coktel Vision games from the same time period that support that specific card. Unfortunately the full version of Gobliiins does not seem to support the Intersound MDO and thus also will not work with Covox.
Some of the games in the mobygames list does not have any soundblaster or adlib support:
Skidoo, Oliver & Company, No Exit and Cougar Force.