Yes, I changed the filename and I also changed the .chroot file

I extracted the file in my PC and I didn't know it mattered, later I found out it was necessary and modified the .chroot instead of adding the extension...

I have
IMGFILE=/home/user/MyDocs/debian-m5-v3b.img
IMGFS=ext2

And if I didn't say it before, it's just great the work you are doing! Having a full debian in the phone is priceless!! :-)