All the international standards for 5.1 systems agree that the centre monitor should, where possible, 'match' the left and right monitors. The best way to ensure a match with the left and right monitors is to use exactly the same monitor model. In the case of GENELEC's 2-way monitors, the cabinets are compact enough so that the standard models can be used in most situations.
Dedicated centre channel versions of two-way systems are more costly to produce, physically larger and have acoustical 'features' that seriously compromises the sound quality. Only in larger systems, for example the 1038B and 1034B, are centre channel versions, 1038BC and 1034BC, a viable solution acoustically, practically AND economically.