UCCNC has settings that Mach3 does not, and Mach3 has settings that UCCNC does not, so you're never going to get a 100% ready to run profile by importing your Mach3 profile.
I've always thought it's a bad idea to use an .xml from someone else with Mach3. If you setup the machine yourself, you'll know a lot more about your machine, and how to fix problems that come up. If you just want to import a profile and hit run, you're at someone else's mercy when it doesn't work.
Teach a man to fish......