normally it looks like this;
AFM1: 3.21v
AFM2: 3.11v
what you do is get AFM1 and run that to your airflow meter, then run that signal wire to AFM2 input on the ECU as well so you get;
AFM1: 3.10v
AFM2: 3.10v
so they will both read exactly the same. if you check the SAFC2 they also support duplexing and halving of airflow meters, that is run twins on a single afm ECU or a single on twin AFM ecu, you get a choice of average, add, or single outut signals, ie
twin z32s to a single AFM input, ie: twin z32 on a GTST PowerFC
single q45 to twin AFM input, ie: twin q45 on a GTR PowerFC
can either bridge the wires, or use the SAFC to manipulate the AFM signals if you are worried and want to be sure its 100% ok, but the wire method is essentially the same thing, it will average them both as AFM1 and AFM2
at least this is how ive understood and gary has explained it