I respectfully disagree in regards to the 9500 being better than the K7XX in sound quality. I had both side by side for a good while, just not at the time I wrote my K7XX review. While the 9500 may be more present in the mids and highs, it is still a less refined headphone. Also, the K7XX was not tuned to be a bright headphone (as the 9500 is). A fairer comparison in regards to sound signature would be with AKG's K702 or Q701 (also leagues above the 9500). What you describe seems like pure frequency preference rather than quality.
And as for the bass having the quality of Fostex, that's quite a bit of a reach. I also had Shure 1840 pads on mine and, while the bass was great and nicely present, it was NOT anywhere close to the quality of the TH-X00. Mind you, this is quality I'm referring to... not quantity.
If you want an upgrade in the K7XX price range but with more present mids and highs than the those I'd suggest reading up on the HE-400i. Mind you, that comes at the expense of a flatter (yet still good) bass response. They go for around $250 brand new these days.
I am not an audiophile other than in wanting audio gear that gives clear and detailed reproduction of sound in a manner that is engaging and interesting, neutral or anything trying to approach neutral is not my preference. My preference for an ideal headphone would be more detailed and accentuated in sound than neutral but not overtly so, with nice detailed highs, mids, and bass - basically a STAX Lamda. I picked up the AKG K7XX to try them out for use with gaming. They just are not a headphone I would ever like - they come across boring and slightly veiled to me. Maybe I just don't have the equipment to really make them sing, but I wasn't going to spend money to try and find out when they really didn't hold my interest after trying to get use to them.
I don't like 'refined' headphones...reason I love the low end STAX Lamda's I've heard and haven't really cared for the SR-009 and SR-007 I've heard on a high end setup at all - just don't like how they sound in comparison to the Lamdas. Once I got the SHP9500's and really listened to them it was 'how soon can I get rid of the K7XX!". The K7XX just never grabbed my interest from the start, and the more I tried to listen to them the less and less I liked them - they just don't do anything for me and were the most veiled sounding headphone I have had. Trying to force myself to listen to them just made me regret my purchase more. Maybe technically they are a better headphone than the SHP9500, but my ears love the sound of the SHP9500 and just doesn't like the K7XX sound. I do love the build quality and fit of the K7XX though, one of the absolutely best designs as far as wearing comfort goes for me.
In regards to comparison with the TH-X00 Purplehearts, I was meaning the SHP9500 with defoamed Shure 1840 pads had
qualities that very much was like listening to the TH-X00 PH with pads similar to the ZMF Ori. Comparing between the two, they do have a very similar sound signature in the low end. I often wear the SHP9500 much more than the TH-X00 because of similar sounding low end but better mids, clarity, detail, and (most especially) comfort. If I want to jam out to bass heavy electronic music it will be on the Purplehearts, but for nearly everthing else I enjoy the SHP9500 just as much and it's much more comfortable. I will be modding the TH-X00 for better clarity, detail, and comfort though... love them too much not to.
All in all, I just wanted to say if someone really likes or love their SHP9500, and is interested in the AKG K7XX, definitely get some listening time with them to see if it's something you would like... the two are not similar sounding headphones. I don't know how varied a persons acceptance of different sounding headphones are. My acceptance is in a range that basically falls from pad rolled TH-X00 PH to a STAX SR-L300/500... Anything with less clarity, detail, and mids than TH-X00 with Ori pads would be a no go: stock pads are a no go for me on the TH-X00 PH...