You _NEED_ USB, gameports overheat and cause erratic outputs. However, as you probably do not wish to get all new equipment, have you tried adjusting the deadband on your joystick within Aces High? This will create a deadband around the center of your joystick so that small spikes won't be registered. Then again, you lose that area of your joystick for input too. Dampening will slow down your joystick's responses, which will help make spikes go away- but it will make the responsiveness really mushy in the game.
If you want the best game port, you need to get a game card. Those are much better than any sound card gameport.
-SW