I am dealing with a sound problem on my Haunted House also. Did away with all the old boards and replaced with PI-80 from FLIPPP. All works on the machine except the sound, which played for awhile then not. I pulled and reseated the edge connectors, etc. so I am going through some of the same diagnostics as you. Did you ever resolve this issue? If so, how?

I was considering my next step being to replace the sound board and aux power supply with a new board from FLIPPP but with the virus stopping or delaying all shipments I am trying to make due. Saw a FLIPPP sound board on EBAY at 2X price of FLIPPP from BigDaddy. May have to bite the financial bullet and head that direction. Before I do that though I will need to check speakers and power.

Any updated advice on your experience is appreciated..