System described above works great but no matter what I did, I couldn't get rid of high-freq noise in the Power Acoustik PEQ-71 which is a combo graphic equalizer and amplifier. I tried re-routing grounds, installing noise suppressor capacitor in power lead-in to peq-71, and even a ground loop isolator on the leads from the computer to the peq-71. the ground loop isolator got rid of the popping and crackling but not the high-freq. The fix was to dump the audio output from the computer into a Sony CD player (automobile type) which has an aux connection on front - no noise whatever. I think some of the observations on this site addressed to noise suggest that a cheap amplifier may not respond to all of the usual fixes, and at $35, the PEQ 71 was cheap. Ah well.
Forget what you see above. problem turned out to be defective coax. even though it is very unusual, once in a while a coax will be shorted out at the RCA plug. that was what was wrong here and there was NOTHING wrong with the PEQ-71 , sorry Power Acoustiks. Your product is just fine.