What do you mean by this?
I've given a MK1 a good listen before from a friends rig at the same time there was the 507 before I decided on forking money on another of HD800's. The 507 ain't no slouch and is the current flagship of the Lambda frame series but for me it just had an annoying treble range, the MK1 in comparison was just better in regards to all sound aspects fairly balanced to me ears. I couldn't afford an MK1 + amp at the time so I got another used HD800 for cheap to play around.
The SZ3 I believe is another version of the SR-007 that is slightly different to the original MK1's (sorry I'm not familiar with these revision codes), but spritzer or any other owner should provide a more reliable response for you regards to the different sounds and tonal signatures of the SR-007's.