[Mayhem]

The two jacks may be wired in parallel to allow "daisy chaining" of the speakers. If possible, I would remove the back panel and check this.

Whilst you are there, you may be able to see the speaker rating on the magnet or on a sticker inside the box somewhere. Impedance can be roughly worked out with a multimeter. An 8ohm speaker will show about 6ohms of resistance on a multimeter. However, this is not going to tell you the wattage.

The pot on the speakers is not something that I have had much experience with and it may either be volume or tone. If it were volume, I would be inclined to set it at 80-100% and drive the volume from the desk/amp. I think that they would be used more if you wanted to balance out the sound in an odd shaped room or one where you hade speakers in separate areas. Again – have not really seen these outside the home entertainment arena.

With the inverter not powering up the amp. As you have said, it may be the inverter but I also wonder if you have powered ti up via the mains supply? You may find that there is a ‘switch’ somewhere that selects either AC or DC inputs. Again, a bit of a wild guess here.

Given the age of these boxes, I would contact Shure and tell them that they are still going strong after all these years but you would just like to find as much information on them as you can. You never know, they may send you a new set and take these to display in their head office. Don’t laugh; I have seen this happen before.

Hope this helps.