My friend had a Trimix eons ago, and he had some channels modified to a higher frequency, perhaps it was 20kHz, dunno. Anyway, it wuz very nice. What frequency were you thinking of out of interest . ..
I wanna do the walter sear thing. His Avalon console has a 30K shelf that when you kick in, it's like woa!!!! Yes we can't hear 30K but you feel it and the harmonics it brings out are cool. So maybe something like that.
I am not positive on the frequency yet but, I am certain I will be changing it so that I will be boosting or cutting a frequency other then 10K that is also higher then 10K