Hrmmm. Well, considering Co-Axial speakers are generally neither LOUD and CLEAR, that's a toughy. My Volfenhags had decent sound for a while, but their durability is that of a piece of ice in a heat wave.
Really, for loud and clear, although lacking in mid-bass, check out Infinity's Co-Axial line. Beware, they aren't very bassy, so don't try to push them to do so, they aren't designed for such.
Have you listened to Boston's SL80? It fits a 5x7 opening, but is not co-axial. It's a plate speaker with 1 inch tweeter next to a round 5 1/2 inch woofer. Crossover is mounted in back. Retail $299; check auctions. 60 W RMS; 200 W peak.