You shouldn't be doing that many crunches to begin with. Do weighted crunches and work them hard like all your other muscle groups.
I think 99% of those ab machines are junk, they usually end up collecting dust.
You just need a better ab routine. Try doing some weighted crunches, reverse crunches, hanging knee lifts, weighted swiss ball crunches or my favorite (see below)
Start by sitting flat on the floor with your legs out in front of you.
Bend your knees and bring your heels about 12 away from your butt.
Place your hands on the outside of your knees with your fingers wrapped around the front of your knees.
Lean back until your arms are stretched straight out.
Now let go, keep your feet flat on the floor and try to raise your arms straight up over your head. (Key word "try")
This should be fairly tough to do, hold that position for 10 seconds, return to the starting position, rest 10 seconds and do it all again.
Repeat until you cry like a little girl.
Done properly none of these exercises hurt your neck at all.
Six packs come from low body fat, not a machine.