Sennheiser is one of the better performers regarding driver matching. Of course, the further you go up the product line, the better it gets. Sony MDR-7506, ATH-M50x on the other hand...
I agree and also note that this observation reinforces and supports the point I made: if you spent serious money on high end, or even mid price, headphones and got a pair with audible level mismatch then you have a defective product - get a refund/replacement. Throwing good money after bad is not a rational solution.
If you have a pair of Sony MDR-7506 or ATH-M50x (or similar) and can detect mismatched levels....it's the same! You have a defective product. Just look at Tyll's (and others') measurements on these kind of headphones - perhaps they aren't audiophilia fashion items but the manufacturers do actually manage the basics like getting the output levels well withing the range of our ability to hear a difference, and also measurably
pretty much identical.
If you spent $150 - $250 on unsatisfactory headphones and you have *another* $250 spare cash to correct the problem...then you just bought the wrong headphones. You should have spent that extra cash on some headphones that actually perform as advertised. Like the err...uuummm... Sony MDR-7506 or ATH-M50x or Sennheiser Momentums. You even have enough to put down a deposit on some HD800s and pay the rest on a monthly plan ;-)