I think you mean LG 47 la 7400 vs 47 la 6200 as there is no LG la6400 except the LG GA6400

So If you mean LG 47 la 7400 vs 47 la 6200

So the only 4 differences are on:

1-LG la 7400 is Edge Led while the LG la 6200 is Back Led
2-LG la 7400 is having sub-woofer inside while the la 6200 is not
3-LG la 7400 is having 3 way speaker while la 6200 is two way
4-LG la 7400 is having a light logo while 6200 is not

Best Regards,
Migo