I use the carlsbro active subs and to be honest 1 mackie 1501 is better than 2 carlsbro 15/600 subs but for me it was a simple weight issue the carlsbro were lighter and with the two they do the job admirably just not the thumping floor moving capability of the mackie imo.
i think the rig looks nicer though with the carlsbros than it did with the big brick like mackie also like the look better with 2 carlsbros than 2 mackies ........ just my personal taste.