Sorry, i didn't speak dialect but can understand it. Coz my parent family from North China not true local Jiangxinese, they speak mandarin. U knew the China is a big country, it's normal for Chinese family transfer from one place to live in another place. My grandpa was a PLA soldier in Civil War, his family following Army from ShanDong province => ShangHai city => JiangXi province, finally set home in JiangXi.
At the north of JiangXi province, there's no uniform dialect usually one city & one region has their own dialects like NanChang dialect / JiuJiang dialect ect, but at the south of JiangXi major Hakkas language coz many Hakkas ppl living in South JiangXi and North GuangDong provinces.
In NanChang dialect, 赣江 called "kong jiang" u r right.