They probably say that because it is quite forward so close to the action compared to Lambdas, but sound-wise it is not too much like a Grado. For example, the highs don't have a tendency to sound harsh (they are smooth and extended) and because they are stats it means better speed, too. Also, I noticed that stats do represent 'air' very well compared to other phones. With the SR-X Mk3 the highs can be a bit of a problem if the source or recording is not up to their level but in a good system they will sing.
So I would say there are probably very few headphones similar to these (I read that some very rare orthodynamics like the Fostex T50V1 are similar to the SR-X Mk3).
Graham, you might want to replace the adapter with an SRD-7 Mk2. Or there are some modified units on sale in the forums as well which are probably even better, one of them has a normal bias connector which you need. It will sound a quite a bit better than the SRD-6/SB no matter what speaker amp is used. There is a nice, long write-up about the SR-X Mk3 here: http://www.head-fi.org/forum/thread/172611/long-meandering-comparison-of-stax-404-and-stax-x-iii-episode-i
Edited by padam - 6/4/10 at 2:21am