Yes, i feel your pain..
Hook up the HD pack, and then plug only the Green output from the HD pack to the Composite (yellow) input on your X1. switch the modded bios off and boot to the normal MS dash
This will allow you to enable the HD resolutions you want - 1080i looks like shite for the xbox on the x1, i always use 480p / 720p
Once you enable, the HD resolutions, turn off the xbox and then plug in the HD pack back into your component breakout cable to the x1.. fire up slayers and it'll boot into 480p format.. Yay!
Most all games will boot into 480p, there's only a select few that only support 480i.
One last thing.. There is a hex-edit you can do on the MS-dash so that it will enable 480p in the MS dashboard. I'm sure it's on here somewhere but haven't looked it up in awhile..
Good luck mang! <