hmmmm.... I have no idea about the above post, but reading this old thread I feel the need to update my banksia views / efforts.
I have now been growing for 2 years:
Banksia integrifolia
Banksia serrata
Banksia marginata
and more recently a few Banksia integrifolia 'sentinel', (small leaved variety)...
Since having a lot more sun for my trees, the Banksias are going fabulously.
Even if I were to try and kill them, they'd bounce back with gusto. As long as they get a lot of sun, they are very hardy here. And leaving a full head of hair on them over winter is a really good technique.
I have cut back hard, repotted, cut the roots a lot, etc etc. They are all powering on.
I fertilize with 'Osmocote slow release for natives ', and 'Powerfeed for natives'.
Make sure you read Grants amazingly helpful thread on Banksias. It helped me a lot starting out with them:
viewtopic.php?f=69&t=812
Very happy now, but now my problem is that I have too many.
The only hiccup is if you fertilize with liquid fertilizer and don't wash off the fertilizer from the leaves, it burns the leaves in the sun.
EDIT - In regards to Banksia marginata,
Ash at Bonsai World is growing a million of them. They are a beautiful bonsai, so I highly recommend getting yourself over there to pick some up. If I remember rightly, he said when they were cut back hard on the young trunks which were only a few cm thick, some of them didn't shoot back and died, but the majority that did survive don't have problems since. It was just the initial shock.
Perhaps Ash can chime in here and give some advice on them, but I think he told me not to cut back below the first branch on the first trunk chop, otherwise they sometimes don't recover. I forgot this at one point

and cut back with no foliage remaining, but it shot back happily and is thriving now.
Marginata and integrifolia are the most beautiful banksias.