Nope, never tried the Amperiors, but the 440s are not as Bassy as the HD25's. But in comparison, the HD25s sound unclear and muddy xD
BUT . . . . and thats a big BUT . . . if you really like something and you are satisfied . . . you should keep it ;D I mean, there is always something better but the search neeeever ends. You find something good, you like it....and you think:
"What if this and that sounds even BETTER? that would be awesomness-ultra!!!".
The Problem is, if you listen to the 440s, it could happen, that you don't liker the HD25's sound anymore. Are you a small or tall guy? The Shure 440s & 840s are big . . . not that big but kinda heavy, if you are a small and thin guy. I have a big head, so for me, thats no problem. You can't headbang with them, they will slip off your head xD