Xenons are worth going for much more than carver audio. The other problem with carver is it is digital (over copper, not optical) with unusual sub woofer voltage, which makes it difficult to upgrade without replacing the whole system. The other 2 systems are analog and easier to upgrade piecemeal.
One advantage of the nav screen is you get an audio graphic equaliser that does help improve the sound. Without that, there are limited presets, of which only one is worth possibly using.
IMO, the carver system is adequate, but nothing special. With the top down, it's not an issue, there's too much other noise to hear nuance. With top up, it's good enough that I'm not tempted to replace the whole system, partly because the top isn't up that much. My critique is pretty much along the lines of Mowflow's, adding that the midrange isn't great in that it's rather harsh and brassy.