While my suggestion doesn't match your stated specs, I've spent many, many hours staring down an ice hole and I'm a long-time believer in Vexilar flashers. They take some experience learning to interpret the readings, but once you do, they're about as close to real-time as you can get. And if I can see tiny little perch ice jigs on one, I know I'll be able to see my crappie jigs, too.

Wouldn't you know it, when I retired from the USAF and moved from ND to OK, I loaned all my ice fishing gear to a buddy that still lived there, never thinking that I might actually use my Vexilar FL-8 and my underwater camera here. He's moving out of ice country, so I'm getting them back soon...can't wait to put some technology to work on those dock fish.