Gottlieb system 1 is able to do this because they use the same transistors to activate the sound input as the chimes, in the same way.

You're going to have to reroute whatever signals go to the sound board to the solenoid driving inputs instead - if that means figuring out where the signals go and swapping them to the transistors via hardware or via software is going to depend on your expertise with either method, and with if multiple signals at the same time are utilized.

I took a very quick look at the sound board parts list and it seems like the sound board is semi-smart with a processor and timers, and looks like a pretty wide input (i.e. more than 4 only) so hardware is probably out of the question. Software would be easier.

Watched a couple videos (including yours) of gameplay of both SS and SS2 - unless all the stuff is scoring different things, it's def. doing more than just activating a single sound for each score level (10, 100, 1k, maybe 10k) like an EM/early SS would - couple of different sound effects for some things.

Some of the sounds seem to be ok, but some of them are god awful. No wonder you want to change the sounds!