parasound to a sub

has anyone had a problem hooking a parasound amp or pre to an earthquake sub?
blown 2 sets of tweeters, one in an old pair of bostons and now in a new pair of paradigms.
earthquake had both high level input and low thru Rca and recommended the Rca
used the normal out of the pre to the sub rca input and got a hum that eventually blew the tweeters.
Could it be cabling? or hook up
thanks in advance
john