Regarding the Game Over and Tilt relays is it one or both that are enegised?
These come from A3 J3 on the driver board. Without schematics cant tell you exactly which one but if you follow the board traces from A3 J3 to each MPS U45 transistor. Could be a transistor/s?
Could also be as Nino suggests a connector. Maybe your missing an address or data line from the CPU to the driver board. This could explain why you have problems in two areas (sound & game over etc)
Check the connector between the CPU and Driver board. The driver board connections to the sound board are A3 J5 pins 1, 5, 6 & 7. These our the sound trigger lines S1, S2, S3, S4. The CPU fires the inputs at IC Z13 and the output from this IC signal tells the Sound Board what sound to play as there are more than 4 sounds it also uses combinations of these signals for different sounds. Could be this connector or this IC 'Z13' which is a 7404.