I just never found the HD800 to be bright or thin which are the biggest complaints of the HD800. I tried the Anax mod around a year ago and didn't like it as much. If the serial number is to believe it could be that mine is a real low one (under 500).
As far as the 007 MK1 I would try to see if you can hear it at a mini meet or when it's not too loud (usually when it begins) at a larger meet as the SR007 MK1 could make an appearance there. I have mine paired with a Buffalo III and SRM717. In terms of sound signature if the HD800 was on one side and the LCD2 on the other the SR007 would be in the middle but leaning slightly towards the LCD2 but the bass is not huge in quantity. I think of it as a HD800 with a bit less emphasis on the treble and a slight warmth to the sound and smaller stage. I also find the SR007 to be on a higher level than the HD800 but not by a large amount.
Also keep in mind I'm not driving it to the fullest but a BHSE is a very large amp and out of my price range and a KGSSHV is hard to get unless you know how to DIY (which I don't and many DIY builders won't touch Stax) or if you can find them in the FS which is rare and they get snatched up quick. The SR007 pretty much cured my upgraditis as the only real headphone I would even consider is the SR009 but I'm not paying the asking price for it. Sorry I'm rambling a bit here.
It's been years since I heard the HD600 but it *might* be an upgraded HD600 so would need to hear the HD600 again to quantify this. If you want to PM this further feel free to do so.