One of my clients (a church) had a sound system problem. Not organ this time - they (still) have a Rodgers.599 Seems they also have a DIY audio tech type who installed some new speakers. Initially everything looked okay, except the power amp Crown CT8150 was down. One of the power stages blew - literally with pieces scattered about inside the chassis. ((BTW you need special security bits to access the innards.) Looking further revealed the problem. Their techie ran shielded mic cable for the speaker feeds. (Aside from the speaker line (mismatch) of less than 1 ohm, it probably would have worked). No doubt the amp went into oscillation mode even tho that amp has many levels of protection. He had the input level cranked. Can't imagine how loud that must how been.
Anyway got Crown (Elkhart, IN) to repair the amp and ran good Belden 14 gauge speaker line to the added on spkrs. No problems now for 4 weeks. Amp died
within a half hour of the original botched install.
Lessen - never run shielded speaker feed lines.
Probably not the best idea to run such a low (less than 1 ohm) impedance from the speakers either. I balanced things so that more than one power amp shares the load.
Rgds,
Ed