I'm not sure why my post (made yesterday) hasn't been approved (or why it needed review by a mod -- maybe because it contained a link?) but you can make this board work with a TTL signal.
Out of the box, this board only supports TTL with 8 colors. This board has pinouts for R,G,B, Hsync (horizontal sync), VSync (Vertical Sync) and signal ground. There have been people who have used this header on the board to get 8 colors from a TTL source.
In order to get 16 colors, you need to augment it with a breakout box that runs the intensity pin through a resistor network. The IBM CGA's TTL output (not sure if the Apple is the same) has signals for R, G, B, Hsync, Vsync, and Intensity. You need to route the Intensity signal through some caps / resistors to boost the voltage of the RGB lines, when intensity is high and then feed the final signal into this board's VGA input (15 pin) to get 16 colors.
I have this board, but have not had the chance to build the breakout box that does the intensity accommodation, so I cannot speak to the final quality of the signal. Based on the pictures of others who have done this, it looks acceptable.
If you give me a couple of days, I'll wire this up and tell you what the results look like coming from an IBM CGA TTL output.
