The part that was making me worry is on this picture:
There you can see how MOSI and MISO are connected on Arduino side over capacitor and resistor -- I can't use those two pins to interface normal SPI devices.
But my problems may be solved with this work here. There seems to be self-made SPI protocol to interface those rotary position sensors: http://interface.khm.de/index.php/lab/experiments/rotary-positionsensor-mlx90316/
I need to test it out though.
PS! Sorry about misleading 'transistor' -- it was late night and I'm not very good at electronic words in English.