And so much for the need of tone defeat buttons , with competent design it’s not an issue and never was .
I thinks it’s one of the bad fashion the audiophile era brought to the table , if every true audiophile press the bypass button why spend any effort on the tone control circuit it . For added consumer satisfaction it can even be a bit noisy so the dear audiophile can feel good and hear the difference when used
Will keep an eye on the used market , this in kind of obtainable.
Go find some Luxman pre amps of the era