Noise when using SPI LED driver on 2m cable?
You did say the crosstalk  fails miserably, but not where it was messed up e.g. the SPI channel for characters, the segments or crosstalk or aliasing.

Each LED segment is an input, but driven by an open drain that should be high impedance when dark. But cable coupling capacitance of 30pF/ft or 100pF/m est. at the mux rate is causing cross talk along with PWM dimming. 

The SPI is driven by a bipolar driver so it is 50 Ohms or so. The PWM could be not bipolar driven but the rise time = 0.35/f-3dB can be used to compute the crosstalk signal current equivalent with the perceived ghosting you see.


1 Assuming you have a clean supply , you can try to reduce the common mode noise by earth-bonding the shield at one end near the DC power source.
2 Then you can reduce the Off impedance using segment driver pullup resistors such that the cross voltage you compute above times the resistor you choose results in noise &lt;&lt;5% current or better.  THis also reduces brightness, so some tradeoff is needed such as 1kOhm.
3 You can use the DC Iset control for dimming instead of PWM.
4 Isolate the PWM drivers from the SPI cable.
5 Most important: Terminate Twisted pair  SPI signal with 150 ~ 220 Ohms and confirm signal integrity.  
6 Try adding a series 100R/100p RC snubber to SPI signals.  Failing this show photos of signal integrity with schematic using twisted pairs for each signal.
etc.  


Matched impedance becomes critical for long fast rise time signals.  Cable Impedance matters.