Hi,
I haven't been able to get the Sapphire to output more than two channels
through Pd (though it is supposed to be capable of 8).
I have tried making a multichannel patch, for eg [dac~ 1 2 3 4]. All that
happens is I get a reduced signal from my 1 and 2 channels coming through my
3 and 4 channels.
I'm satisfyingly using a Saffire Pro40 on Linux with Pd too, had an installation with 8 channels working flawlessly.
Your issue, as IOhannes said, might be about the internal configuration of the soundcard.
Since you are on Mac, have you already tried to setup the Saffire MixControl?
Basically, you only have to setup the Line Outputs to 8 DAWs, then set eight channels outputs in Pd.
cheers,