Gameport adapter

Hi, i'm currently building my own Flight Simulator cockpit and i would like to use my usb to gameport adapter (not a cable/plug) to plug my switches. The problem is that I dont know how to get more than 4 button with my adapter. In windows it show 8 button but depending on the mode (the button on the adapter: Wheel, gamepad, joystick) it light only 1 to 4 button or 2 button at the same time like button 4 and button 8. So i think I need to use like resistor to make a difference when 1 or 2 button is pressed so the 5,6,7,8 button light up along.

Is there anyone who can help me understanding how I should work?

That may simple be the way your joysticks function, you could always pick up a second USB gamepad, basic USB gamepads are extremely cheap, and can often be found in second hand stores, no adapter required. You can have as many buttons as you want by just using more gamepads.