I was in rehearsal yesterday and tried one thing:
I connected the Send from FX Loop to my interface for the DI signal, piece of cake.
Then I stuffed a guitar cable in the Return. There was a big drop of volume, but I could still hear a little treble from the speakers, but I still had some annoying humming noise
Is this bad for the speakers, or is this a way to do it?
I wanna try some IRs at home with my 5150
Oddly, it looks a reasonable approach - keep the master volume at 0 and pick the IR (just don't unplug the speakers). You'll lose any of the power amp characteristics and it'll just be the pre-amp section, but you know that already.
I await correction by those more in the know.