Thanks for the responses, gents. (Franc- you have been constantly responsive to me in the past, for which I thank you).
Interestingly, I had the compressor wired to a separate receptacle, connected via very high grade wire to a separate breaker in a separate subpanel from the subpanel which services the audio system power. That, alone, did not prevent the 'zap.'
I then plugged the compressor into an outlet on my 240v stepdown transformer, which seemed to reduce, but not entirely eliminate, the zap.
I then plugged my electronics- all of them- into an Shunyate Hydra, which, combined with the stepdown transformer hook up for the compressor, seemed to do the trick. But, I will contact Scot Markwell for this zero switch relay kit, since it will enable me to have a little more flexibility in how my components are hooked up. Regards,