How are McIntosh C46 tone controls different?

If you look in the manual pg 22 it shows the frequency curves for each adjustment. I think the highest frequency tone control is centered on 8 kHz. Some say that's whre the typical harshness is. In my experience it wasn't or at least it didn't tame what was bothering me. For someone concerned about highs I would suggest either the C45 or the c2300 (also pg 22 of the manual) which have standard treble single-knob adjustments. I ultimately went with a c2300 for the tube front end and found the treble worked well. The Mc gear already does a good job with highs and ultimatly I found I didn't use it all that much - maybe on no more than 10% of my recordings.

I find that I do not have to adjust it very much if at all. It seems to do a great job without a lot of adjustment, but it is nice to have if needed.

OK, thanks for that. From the manual page,it looks like the highest control is centered at 4kHz, as the label says, not 8.
Aren't normal treble controls mainly for 10kHz+?

Yep, that's where I think the confusion lies. You can take a look at the treble response and see it doesn't really take off until above 5 kHz or so. The equalizer tone controls on the c46 are more for tuning room effects than adjusting the highs and lows generally. I was going to buy a c46 until I realized the equalization controls had a different intention than the single treble control.