I have one of the V6's that I bought at a consumer hi-fi store to go along with my other eight 7506's. They do seem to be pretty much identical, except for some of the "artwork/printing" on the unit.
The only difference I've found so far, is over the years all the "leather" (naugahyde?) on the ear cushions on the V6 dissolved, leaving just the foam underneath - which hasn't happened on any of the 7506 units. But that might be coincidence, or no longer a problem with more recent models.
If you can, in fact, get the V6's at a deeper discount, go for it. Even if there are some slight performance discrepencies (that I haven't noticed), no one buys 7506's for accurate hi-fidelity anyway - we get them for their isolation and because they are LOUD! The V6's do very well in those departments!