They both look Nice. I assume you plan on tying the trackball/spinner into the player1 controls?

The only suggestion that I could make is MAKE SURE you mount your joysticks EXACTLY perpendicular to the player's normal standing position. We had slightly angled ours to let ppl stand slightly off to the side, does NOT work well at all, had to go in and remount the joysticks. Your brain automatically assumes a 90º angle to the screen. Don't try to outsmart your own brain. Other than that, the 4 player ipac should work nicely. Oh, and the trackballs are VERY expensive. ~$100 US for just the trackball alone, compared to $15 for each joystick.