The monster cases are available even with 6U and 9U. The reason for these additional cases is that the 12U monster cases are a bit difficult to handle by one person only. At least for the double version A-100PMD12 two persons are necessary. On top of this it is necessary to have available smaller versions of the monster cases when they are mounted together as shown in the pictures on the left side (because of stability and appearance - with a 6U case as upper element the construction looks not that "intimidating"). 

Single version of the 6U/168HP A-100 monster case with 6U/168HP (A-100PMS6):

outside dimensions (with front cover, closed state): ~ 90 (length) x 35 (height) x 23 (depth) cm
weight of the case (incl. bus boards, power supplies, with front cover, without modules): ~ 10.5 kg
outside dimensions of the case (without front cover):  ~ 90 (length) x 35 (height) x 18 (depth) cm
available 19" width and height: 6 U x 168 HP
max. module current: 4A (two power supplies 2A each, one power supply is assigned to two bus boards)
inside usable depth for A-100 modules: approx. 70 mm in the power supply area (bottom right), resp. approx. 100 mm in the remaining area (measured from inner side of the front panel until end of the pc board of the module)
position of the mains inlet: center of the rear panel

The new power supply is named A-100PSU3 and has available 2000mA@+12V, 1200mA@-12V and additional +5V with 4000mA. +5V are no longer required for A-100 modules but there are many modules from other manufacturers that require +5V.