Well only a few apps on Xbox actually support command line launching, so you are gonna be stuck going to other menu systems regardless, but by far the most customizable dash is UnleashX.
It is what I use on my machine, and aside from being able to change literally everything about it form a visual standpoint, it has tons of other features, such as the ability to password/passcode any item you list in the menu, the ability to run scripts/batches, and the ability to use command line launching for those emu's that do support it.

That is UnleashX with the skin I created for my arcade machine. The marquee of the arcade machine displays the game, the screen displays the game icon or a preview video, and the background is a great retro arcade fly by video.