Ok, here's where I am at.
Three types of input, transformer coupled coaxial, optical, and TTL. After this input, there is DC blocking cap for the TTL case and then this is fed into a buffer that can be configured to have gain. This performs the optional level shifting from TTL. Then into parallel buffers that drive the output. There is also another DC blocking cap after, that might be used depending on the final configuration. The output can be taken as TTL, transformer coupled coax, or optical. A voltage divider plus series resistor allows for proper termination into a BNC connector.
So, in my case I'll use TTL -> TTL. But this could be used for a coax -> optical, optical -> coax, ttl -> coax, ttl -> optical, etc.
Perhaps now there might be a bit more discussion?