My question is how do I wire it up?
Like JustMichael said, ipac is not designed for analog joysticks. If you want an analog joystick, hack a PC analog joystick and attach the happs to the PC joystick.
Is it the same as wiring up a regular 8-way? It looks like there are 3 terminals on each pot.
Do I use all 3 or just 2?
Should I buy the optional pot amplifier or does the stick perform adaquate without it?
No,
All three (I think), and
No, if you use the hacked PC joystick's POTs to replace the happs POTs, or use the happs POTs on the dual sidewinder gamepad others have hacked.
I've never hacked a joystick, so take my advice with some salt. But others do the hacking analog joysticks a lot, but mostly for wheels/pedals or StarWars yokes. You'll find the info somewhere on this site.