As far as I understand it the value of CC61 is just the lowest bit (least significant bit) and it is encoded as 0 (==0) and 64 (==1).
And “yes”: it is completely undocumented. Neither the manual of the Peak or Summit documents it in any detail.
In the mono station manual it is also referred as CC(8), but also without any further explanation:
CC(8) denotes a CC pair where the second CC is used to create an 8-bit message for a 0-255 value range.
Its annoying that CC Values get send after Pattern switch.
But thats another chapter…
I just tested this on my Syntakt and here is how I got it to work with my Novation Summit and Filter Frequency (CC pair 29, 61).
On the AMP/CC Select page: set SEL1 to 29 and SEL2 to 61 (the CC pair)
On the FLTR/CC Value page: enable VAL1, which will control the value (VAL2 has no effect)
So this doesn’t give any finer-grained resolution using the pair, but it totally works!