Mike,
Just as Donny says, I would not hold out much hope of Technics rushing to improve the vocal harmoniser on the 7500.

I owned the kn5000, which to be fair did not have a harmoniser on board at all. You had to buy a seperate digitech unit. I always found the mic input on this board ok as it stood but then I am not a pro.

I then moved up to the 6000 and there was a built in harmoniser which was the most dreadful waste of space you can imagine. Real 'toy' stuff. Disgusting really to include it on a high end keyboard at all as it was totally useless even for home play. Anyone attempting to use it live would have been laughed out of the gig.

As a dedicated technics fan we all waited for the 6500 feeling sure that our loyalty would be rewarded and that technics would address this issue. Did they fiddlesticks. Same old same old. Then when the 7000 came out with exactly the same sh...... 'unit' on board I bought a 9000 pro and left technics behind. Do I regret it....not for a minute.

There was a lot to like about technics boards but if singing is your thing and you want decent onboard stuff then steer well clear of technics.
Very best to you
Tony W