I have had to replace several duplex outlets over the years. Definitely two wire open ground. There is an addition on the house, built in the 1980's. Those outlets do have the typical green grounding cable, but the breaker box (since replaced and upgraded) was still from the 1950's and didn't have provisions for actual grounded outlets, anywhere in the house.
I don't have access to the model number of the Panamax surge protector, but it's a fairly low end model. All I know is when the amp was plugged directly to the mains, it's metal front cover conveyed some minor current flow and when plugged into the Panamax, it was resolved.
I am not in a position to rewire my entire home either DIY or via a paid professional. I also don't own equipment anywhere near true audiophile or reference level cost or performance.