ok, here's the deal. A bios runs in the background. Just like on a computer, you can flash the xbox with all the bioses you want and it'll keep booting the normal M$ dash.
You have to configure this bios to boot the dashboard (like an operating system). Now, i think all bioses will default to D:\default.xbe then it will look in 3 other places specified by the user and last the default M$ dash. So you have to configure where your dashboard files are. Easiest way to do this with the xenium is to use the xenium FTP feature and ftp a dashboard to your C:\ drive or your E:\ drive or where evever (most people put it on C:\) then configure your bios to launch E:\avalaunch.xbe or E:\evox.xbe or what ever dash you downloaded (I recomend avalaunch) Then your set.
Also, only use evox M8plus since you have a 1.6, so far it's the only bios that works for you. http://www.xbox-scene.com/bios_retail.html
That site has the bios list options and such.
To edit the bios you use some program, i know for most bioses it's XBtools but i beleive M8 needs sumtin else. Search around i'm sure u'll find sumtin.