You want to make an RGB cable. The difference is amazing!!
You just need to find the pin outs for each (I have them around here for the amiga side somewhere if you need them, but not for the monitor).
The RGB port on the Amiga has both digital and Analog Red Green and Blue signals off the 23 pin port. Use the R,G,B analog signals not the digital ones

Also, if you can't find a 23 pin connector, you can just get a 25 pin one and grind off 2 pins from the end of it. Not pretty, but it works.
Good luck.
AmigaGuy