Here's the way things should work. You create a boot CDRW with evox as default.xbe, the evox.ini with the right IP addresses and the back-up folder. The evox ini should be edited to just have the format choice - or to include the format cmds. Put the new hard drive in and the boot cd in. A xbox with an active mod chip will always look for a boot CD first before trying the hard drive boot. So, if the xbox likes your cd, it shouldn't matter if it likes your hard drive. It took several reboots before it actually decided to run my disk.
** EDIT ** - I'm not familiar with evox 2.3. I'm comfortable with D6.