Dave,
Sorry I miffed you - this is a great thread, BTW, and, indirectly it IS a debate about DSB or BB, BUT, the difference is, and we all recognize is respect for each others approach.
So, that being said - Herman, my first two tanks (30 and 90g) I ran all three systems (Jalabert - DSB, Plenum, and Berlin - Skimmer). In the 90, I went a little extreme and NEVER had any problems with it. Matter of fact, I am attaching some pics of the tank when it first started. You can see how deep the sand bed actually is and here is the specs - 2" plenum just about covered the entire tank. 2" of course aragonite and 5" of southdown (about 250 lbs fresh and about 45 lbs seeded from my 30g).
For those of you who remember the 90 in it's day, that tank was OUT OF CONTROL teeming with life, growth, health etc.
I also had sand in the sump in the chamber between both baffle sets, there was live rock as well as runnle and a HUGE star fish.
Shaun and I discussed the option of going external with DSB - again, only thing I noticed, was that it took some time for my tank to start top show color and growth - that is just now happening - and Ill say again, I just noted that my sand bed in the fuge is teeming with pods, is bubbling and starting to get the colors in the bed.
House