I got an answer from SD on why they didn't include 4 mic inputs:
Wayne,
Size, power draw, and applications are the chief reasons we kept the product to
two mic inputs. From our research, when an application requires more than two microphone
inputs, its complexity and routing needs benefit from a full-featured mixer--like
our 442--or from a product that has extensive mixing functionality--like the larger
workstation recorders. For many applications, including two booms and two wires,
the 744T is a great fit (two 744T's are smaller and less expensive than any of its
workstation competition).
For applications where you need more that two microphone sources, yes you will need
a mixer with the 744T.
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Not sure I agree with the decision, but there you go...
Wayne