From the examples I've heard, the A-106-1 is every bit as capable as the v.1 MS-20 filter (same as both MS-20s I used from the end of the 1970s to the mid-80s, then from the early 90s until this past year) which is the same as the Mini (and, I'll also note, the Mini sounds like that first MS-20, fresh out of the box in 1979; many people claiming the Mini doesn't sound like a 'real' '20 are not taking component aging into account and probably have never heard one back during its original retail availability)...and those are super capable when prodded the right way. It can boom like a mo'fo in the low end, sound bubbly in the mids, and tear your head off up high. And yes...that's the point behind the A-106-1; Dieter wanted a Sallen-Key pair that was 'more'. The insert point evilness is just the cherry on that cake, but having all of the FM capability already puts it beyond the MS-20's Sallen-Key pair.
One other thing...if you're doing the Rackbrute, have you considered coupling it with something like a Minibrute 2s? The pairing is a natural, plus since your 6u is all voice, linking it with that sequencer + some extra patchpoints for $649 seems like it would make sense. It's definitely on my list to do here.