A lot of recommendations to be found concerning the stacking order for two stacks, so here my experiences with three stacks.
I have chosen to use three stacks, as this is less high than two stacks and as such more appealing to my eyes.
I use a custom made rack for some years now. When it was designed, I did not consider free hanging Burndy cables but wanted the rack to be as low as possible. In hindsight maybe not the best of all design decisions, but still I really like the look of this rack and it sounds quite good.
Based on many helpful threads and comments on this forum (thanks everybody) I tried several options and now found this stacking order to deliver the best sonic results:
300 DR Head
552 DR PS
Tuner and Laptop
(and an old backup CD player hardly used)
Hidden behind the right stack are the power supply for the tuner and the USB-SPDIF-converter.
This stacking order allows the 552 Burndy to hang free, the 300 Burndies are supported by the solid back wall (some layers of flexible packaging material between the cables and the wall), the 555 Burndy is supported by a sponge on the floor.
Prior to this setup, I tried configurations with 300 and 555 Burndies hanging free, but this came with the drawback of the 300 head not located on the brain stack.
So it seems for my system the best compromise is to have priority on brain/brawn separation and free hanging 552 Burndy.
Happy to read your comments and suggestions, cheers, p.