There is a SP write up for the older version Six-Axis in this forum section, it's back on page 5 now.
http://forums.xbox-scene.com/index.php?showtopic=636987For your 3rd party controller you'll have to open it up and see what type of sticks it uses, but no sticks from any official Sony controller are going to work in it because Sony uses a smaller type on the older controllers, then switched to a newer Hall Sensor type on later versions.
Most 3rd party controllers use a similar type of stick to what the DS2, XBOX and 360 controllers use though, so you should be able to replace them with any of those, but you'll have to open it up and see to know for sure.