Well, the S7 does not really sound "bad" in any way. But honestly it pales in comparison with my Huawei Mate 8 as there is a very notieceable difference in favour of the Mate 8. The difference is I get amazed by the Mate 8 and get chills down my spine while listening to music becuase of the depth of the sound. I don't get the same feeling at all with my S7 as it does sound flatter.
My iPhone 6S Plus, Lumia 1520 and S7 Edge are about in the same league overall with some differences. The Mate 8 easily and clearly has the better sound than all of them. It even has slightly better sound than my Meizu Pro 5, which has an internal DAC and amps. Both Meizu and Huawei stand above all other phones I've had, but the Mate 8 has the slight edge between the two of them anyway. The Meizu has a lot more power to it though and volume levels go crazy high.