Hi I have a Frantabit and love the Bit Depth fuzz sounds too. There are many ways you can try to decrease the high end. 1) buy a Xerograph or another Low Pass Filter, 2) run a sub octave into the Frantabit with the dry signal turned down 3) running the Frantabit into my DHA valve overdrive tames it a lot so it sounds more like a grainy fuzz or a broken radio
The one disadvantage I find with the Frantabit is unless you have a high output signal or a boost pedal or a compressor/sustainer infront of the frantabit the Fuzz sustain decays quite fast if your planning on drawing out the note. You most likely already know this. Have you tried the Oxide? Apart from the "fwapping" attack noise some people are not keen on, the Oxide can come pretty close the Frantabit unless you really like the extreme Bit Depth crushing noise all the anti-clockwise.
My recommendation then, try finding a cheap second hand DHA VT1 pedal to try out?