well normally for evox to use trainers in general... all u have to do is make a folder called "trainers" whereever evox is booting from (normally on modchiped xbox's it's in the C parition)
then in the evox settings make sure the TSR is set to "normall".
if u did this correctly it "should" work... but as for updateing your bios i dont know how u can do that since u said u got a softmoded xbox... unless u flashed the TSOP... which if thats dead, good luck getting your xbox working again.
p.s. i dont know much about softmoding or tsoping... but i would say im pretty good with Xecuter brand modchips and software setup.