Ooh, that's a lot of fish for 1000 gallons, and those babies (the koi as well as the Shubies) are going to grow. Have you considered re-homing some? Winter can be a stressful time for fish as it is.
No personal experience with pond ice where I live, but have heard lots of positive feedback regarding the pond breather. Basically, all you want to accomplish is to keep a hole open on the surface of the water -- this allows for gas exchange between water and outside air. So use of a heater (check energy used), pond breather, air stone.....or a combination.....? I already keep an airstone a few inches below the surface during winter -- just in case

(suspended with sections of pool noodle), but I'd be willing to try a pond breather if it ever came to that.