I loaded the Black Widow in it and friends, it was unbelievable. It had good bottom end to start with but not only did that come more alive, the overall presence was also boosted. To compare, I played with both cabinets and had my wife unplug the extension and it was very clear what a huge improvement there was with the extension. The top cabinet weighs 27lbs and the bottom is 33lbs.
The whole package is just wonderful how it all turned out so if you are thinking of something new, consider Tommy Huff's work. He also builds the rack mount ears so you can just plug in the MB500 and start pickin.
