So do you believe the technical specifications in this case? The Mackie SRM150 is supposed to have 150 W, I suppose RMS, anything else ("PMPO") would be idiotic as a specification. If it does have 150W RMS, how could it be no stronger than the on-board speakers of the S950, which are rated 2 x 15 Watt? Maybe it has less bass, ok.
All these magical wattage output numbers etc, are mostly BS, manufacturers use as bait to make people buy,....I instead only use my ears when I buy speaker gear,

.....if it sounds good to me and fits MY needs I buy it,.......down the road if it don't,....it's gone in a minute no big deal it's only gear.