Improper ground

Okay, I've got a 20A circuit with 5 receptacles in the chain. Only one of the five have proper ground. As far as I can determine it's the first one in the chain (has a switch also, which btw when I turn it on/off a "pop" can be heard from my speakers). I have a 7 outlet power strip plugged into the grounded receptacle, which comforts me and where I plug my modest gear into since it's grounded.

All the receptacles in the circuit are getting exactly 123 volts each.

By plugging my amp straight into the improperly grounded outlet what are the risks here? Damage to the amp from normal every day usage (don't believe so). Should I get an electrician in here and ground the outlets.

I'm interested in whether I should be concerned with plugging my gear into non-grounded power socket(s)...