I wouldnt say im a very smart modder but i just but xbmc on my box and had the same problem I just renamed the default.xbe to match the dash my bios was bringing up (in my case evoxdash.xbe) That worked great
I would back up though if you havn't already
So if you didn't understand that
I renamed xbmc file default.xbe to evoxdash.xbe
then deleted my orginal evoxdash.xbe
then when my bios loads evoxdash it'll load xbmc.
you can also edit your bios with xbtool or something, there you can keep all your dashs and change the order that your bios will load up in