The problem here is a pennies problem being sorted with a pounds solution.
The output is +4dB, the speakers being designed for the lower level get driven too hard - so we're looking at what? Two T-Pads, costing virtually nothing, plus maybe a M-F adaptor to house them? In fact, maybe a small mod and have a small box with two knobs you can then adjust to get the loudness to match the output fader and meters. Is there a reason we've suddenly got very complicated?
Indeed. ATTENUATOR ADAPTOR, -20DB, XLR - PSG02973 - PRO SIGNAL
Can't find any other speccs like input Z but cheap enough for a busk?
Dave.