For less than £150, you can buy a Peltor 8006. I can't recommend them enough. Very comfortable, very clear and with good sound insulation. That they compress into a small package is useful as you can get more into your headset bag!
As for impedance problems, my instructor uses a DC headset and we've never experienced any problems with incompatibility (in four different aircraft). I've heard that any problems can also depend on the intercom hardware as much as anything else. It seems to be very much hit-and-miss.