A portable amp will improve sound quality and make the headphones go louder, but that won't increase the headphones' isolation from noise in your environment. Open back headphones are meant for use in quiet environments.
I listened to these QC35 at the Bose store and was reasonably impressed. Unfortunately, I couldn't compare them side-by-side with the QC25 using the same music, but from memory, the QC35 is less harsh (less spiky FR) in the lower treble, which would be an improvement. Can anyone chime in on this?
I couldn't listen to them. Way too bright in the 5k region to the point of being painful. I think it's fit dependent (ear canal resonances) so YMMV. Amazing deal. I remember getting them for $250 used. That was a few years ago though.
Huh, didn't know that even existed. Thanks for the link. It's still a 4-hour round trip to the border though, so it's not worth it unless I'm going shopping in the US... not likely with the current exchange rate :(