For people interested, there is a rom variant available to beta test (in addition to the Oliver Kaegi mod to do the 7 digits).
6 or 7 digit
extra balls can be set to pay variable points independently from specials
specials can pay extra ball, variable points, or replay independently from extra balls
no tilt through other players
drops only reset when needed (i.e. all up during ball start, no reset needed)
# of credits for hstd settable from 0-5
Main gameplay change:
After completing the matrix table once (72 line bonus is lit) the following occurs:
Any complete disparate symbol line scores 9k per line and leaves the targets down. So if you have the 4 corners as pyramids and you get the center as the eye, you will get 18k awarded since you just completed 2 lines (the diagonals)
Any complete same symbol line scores as follows:
Any same symbol column scores 18k, resets all 3 banks, clears matrix
Any same symbol row scores 27k, resets all 3 banks, clears matrix
Any same symbol diagonal scores 36k, resets all 3 banks, clears matrix
With the right combination of precision shot making, you can get up to 90k extra. (plus the disparate line completion of 9k each along the way).
There was another variation tested that built the lines a different way, at this point I don't remember what the rules change was, but it wasn't as fun as the above.
The additions of no tilt through, and ability to fine tune the extra ball/specials amount were added at the request of tournament directors for more control over how the game plays.