  Within the theory of complex interpolation and theta-Hilbert spaces we extend
classical results of Kwapien on absolutely (r,1)-summing operators on l_1 with
values in l_p as well as their natural extensions for mixing operators invented
by Maurey. Furthermore, we show that for 1<p<2 every operator T on l_1 with
values in theta-type 2 spaces, theta=2/p', is Rademacher p-summing. This is
another extension of Kwapien's results, and by an extrapolation procedure a
natural supplement to a statement of Pisier.
