Ok, I got it working in "slow"-mode.
I indeed put each individual pin either High or Low. It is more of a proof-of concept than it is the end result. The loop now takes as much a 80-100uS with a analogread and normal digitalwrites (16 of them)
Now I know what kind of signals are required to use the DAC, I will try to use one of the ports for a shorter looptime.
I will try to use portC to driving the DAC.
"So what is the difference between a 1 and a high?"
In the digitalWrite help it says explicitly it want either HIGH or LOW so I was under the assumption that those two inputs were the only ones accepted.
More to come.