Hi,
The test is to try and find out if there is a hardware fault on your 7k or if adjusting the sound is enough to improve things. If the problem is specific to certain keys only then it looks like a fault. But to find if a frequency range is the problem here is the procedure:
Initialise the kn7000.
Go the equalizer (now all flat) and switch ON in the bottom right hand corner.
Reduce the FIRST slider ONLY to say -9dB (minus) for example.
Go down to FC and start at say 63Hz, try the sound.
Adjust to the next 80Hz, try the sound.
Try 100, 125 etc etc in turn and see if any setting improves the sound.
IF a setting does improve the sound the next step could be to try the second slider but a much "fatter" Q than 0.1 would be needed to hear a difference.

Again if the problem is specific only to 12 keys this will not help and it looks like a fault. You could try taking out any footswitches, leads etc and a factory reset, hold down 8&16, Rock, Ballad and Jazz rhythm buttons and switch on.

It would not harm to take it up to version 1.6 though whether it helps depends if the problem is hardware or a firmware that somehow got corrupted. If you want to do that leave your email address and I can supply the required 6 floppies.