I find their soundstage to be exceptional. Apart from the isolation they provide, I'd never know these were closed headphones. They put my HD600 to shame in this regard, and nearly all other open headphones I've tried. The only other closed headphone that shares the K550's remarkable soundstage is the Beyer T5p, which is over $1k, and has other oddities to the sound that make it not a worthwhile buy (namely Beyer's dramatic production variation). There are several open headphones that do have a larger soundstage than the K550, but as is the case with the K701, the soundstage feels artificial, everything is blown way back and there's no layering from near to far. HD800s are the king of soundstage both because theirs is large, but it's also extremely well layered so that you can pinpoint both X and Z axis locations. The K550's soundstage isn't quite up to that par, but isn't far behind. I've called them HD800-lite before because they share a similar signature, with K550s having a little less midrange quantity, and the overall sound quality is somewhat coarser, less revealing, and as for the 'lite' - available for 1/10th the price.
Speaking of that price, at least in the US, a K550 (refurbished) can be had for $130 straight from Harmon. It may have a few nicks and dings, but it should be functionally correct and that is the point. I'm sorry you have issues with the headband. I use mine on a small-ish setting of 2-3, while some here are at 8+ (wow!). I don't envy the designers of headphones who have to take into account such drastic differences in melons across all people.