My amp has either speakon, or binding posts for the output, so I think I can disconnect the speakon on the back of the amp and just hook the multimeter to the binding posts. It should be the same thing right? That way I dont need to take apart my speakon. I just wast sure how to measure it, I read that you dont want to hook up the multimeter to + and - at the same time....it could blow the meter. Maybe that was just to measure current. I thought I needed to hook both probes in line on one side of the wire.
Measuring between + and - should not blow your meter. That is what they are for. I measure high current 480V all the time with my meter so you should be fine measuring your amp. You can measure from the back of the amp if you want to and as long as you can put your leads on the contacts. You might have to hold your leads doing it this way though unless you can stick them in there and they stay. If you take apart the connector, you can clip your leads to the wire.
I can't promise anything. I'm just planning now and the actual build probably isn't going to happen any time soon. It's wintertime...
I still might place an order for the LMS Ultra quite shortly. I'm also considering Behringer iNuke NU6000DSP amp for this project.