There's no problems with having different first stages, I think most people have matching sets either because they bought them as a pair, or they like things to be all the same for neatness / standardisation of routing. However I would keep the connection type the same i.e. both DIN or both A-clamp - preferably DIN, but again, there's nothing to stop you mixing and matching. You might get funny looks from the serious techies, but there's nothing to stop you doing it.