There shouldn't be any problem at all with using the R2C as main stereo speakers. The crossover point to the woofer is 400 Hz (true also for the R3), which corresponds to wavelength 2.8' or .85 meter. This should be slightly more than twice the distance separating the two woofers, which means that the two woofers will be mostly coherent until the vertically off-axis listening point is nearly 90 degrees above and below the horizontal. The main lobe will be much, much thicker in the vertical plane than it is with the great majority of other speakers. This of course is consistent with the intent of the coaxial driver. The crossover points are the same for both the R3 and the R2C, which means that it is virtually certain that the crossovers are identical. The only difference that you might notice is a small difference in bass, where the R3 has a slight advantage. You might not notice this difference, however you might encounter a less smooth handoff to a subwoofer with the R2C vs. the R3. Since Kef gives the low-frequency response limit of the R2C as 74 Hz (vs. 58 Hz for the R3), I would plan on needing to cross to a subwoofer no lower than 100 Hz, probably 120 Hz or even a bit higher. (The reason the R3 goes lower is that uses a ported enclosure; the R2C is sealed.) The majority of subwoofers are designed with somewhat high Q, to make the enclosures smaller and to improve efficiency within the band, but the tradeoff is that the response has a broad hump and begins to roll off, at the upper end, somewhere under 100 Hz. You want to pay attention to this when selecting a subwoofer, i.e., you want to study the frequency response plots and choose one that remains flat up to 150 Hz or thereabouts to give you the assurance that you won't encounter a problem in the integration. As long as you pay attention to this, I can't think of any concern with using the R2C as main stereo speakers.