I'm the OP---- re kalali's apt comment: Many of the preamps suggested do not have 4 sets of outputs.
kalali is correct: that configuration is indeed rare. My PS Audio PCA-2 does have two pairs of XLR and two pairs of RCA outputs, which I use to drive two main amps [separately] and two pairs of sub-amps. However, it does not have two pairs of XLR inputs, but only one.... thus my search.
In any event, thanks for all the suggestions.... they are much appreciated.