If you compress/limit during transfer you will need a deditated 4-channel compresser and the ability to lock them togethr so that every track is compressed equally at the same time, or you will destroy the image.
Oh - and make sure that all four inputs are set to identical levels - IE: set the level according to the loudest level on the loudest track and then set the other three to idectical input levels - otherwise you will destroy the image.