Se and sline have diffrent seats
I have 2006 a6 3.0tdi sline lemans with sline seats. Love them . I have sat in se and yes they are more soft but sline are half bucket seats and they wrap around you nicley , yes they are harder to seat on. Also driver seat has electric lumbar support.
So its all about personal preference ...
If you are not far away you can try mine :)
Also you need to think about ride hight and suspention. Se has standard soft and sline is lovered by 30mm and much harder.