Two thoughts on the subject.

First, check with Outlaw about stacking M200's. At one time, I believe the recommended stacking no more than three of them due to cumulative weight load on the bottom one as much as heat buildup. Four may be OK, but I'd let them chime in .

Second, if you are concerned about the rack being stable, I'd like to know how you plan to arrange your components. If you plan to put a couple source devices (DVD player, CD player, VCR, satellite or cable box) on the bottom and the amps on top, then the rack would be much more likely to have stability problems if you bumped into it than if you located the amps (and the amps' weight) on the bottom shelves. Putting the amps on the bottom would anchor the shelves as well as put the devices that you interact with least in the most out-of-the-way place -- down at the floor. I haven't used any of Outlaw's racks with or without casters, but I'd expect the casters to be a little more prone to moving than feet if the rack is on wood or tile floor (if it's carpet, I would expect little to no difference). Some racks will allow you to fill the support posts with sand or lead shot for additional stability, which would be an effective way to eliminate any concerns about inadvertent tipping.

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