Soundman,
Welcome. About the dual terminals: Check to ensure that the gold links are in place between the two sets. You can use either set, but sometimes the gold links between the two sets become dislodged and don't make electrical contact, which would cause only the woofer or midrange tweeter section of the drivers to operate. That would produce very muffled or very garbled sound quality.
Put your ear close to each driver in each M60 and listen to be sure each driver is working. Use wide-range music with lots of bass, midrange and treble (cymbals, etc.).
Regards,
