The feed system of a spoolgun is foolproof right enough but with that setup, you run into power control problems. Your MMA/TIG inverters are Constant Current (CC), and you'll really struggle to achieve a stable arc with MIG on CC. That's why all MIG machines control on Constant Voltage (CV). I'd like to see someone try one of those "converter" kits and see what sort of results they'll get with it, but I imagine it won't be easy to get anything good out of it. The best options are either: A good quality conventional MIG set up for alloy like I describe, or a MIG power source + regular spoolgun. The OP didn't seem to want a spoolgun.