As it is increasingly important to minimize costs and time-to-market when developing polymer systems with improved performance, in-process characterization methodologies become more attractive. Indeed, it is important to make available fast response characterization tools which, albeit using small amounts of sample, are capable of generating relevant data on the rheological response, process-induced material structure and product properties. Recently, the authors developed a prototype modular small-scale single / twin-screw extrusion system with outputs in the range of grams/hour that was coupled to a rheo-optical slit die adequate to measure shear viscosity and normal-stress differences and perform rheo-optical experiments, namely small angle light scattering (SALS) and polarized optical microscopy (POM) [1]. As with most similar attempts, the generation of a range of shear rates implied operating the extruder with varying screw speeds or feed rates. However, this changes the thermomechanical experience of the material inside the machine and, henceforth, may change the characteristics of the material in the die inlet, which in turn may jeopardize the validity of the measurements. To circumvent this problem, the authors adopted a design concept that has been seldom utilized, consisting of a die with two parallel channels, each fitted with an output control valve at its inlet, the total pressure drop remaining constant. While one of the channels can be utilized for conventional extrusion, the other has a slit configuration adequate for rheo-optical characterization. This solution is validated and several case studies are discussed. [1] P.F. Teixeira, J.M. Maia, J.A Covas, L. Hilliou. A small-scale experimental extrusion set-up for exploring relationships between process-induced structures and characteristics of multiphase polymer systems. (2015). Macromr Mat.Eng., in print, DOI: 10.1002/mame.201500196