For motor-only decoders I always go with TCS because of the excellent motor control. According to their website, the K2D4 is a drop-in for the Kato N-scale RS2:
https://drupal.tcsdcc.com/installation/n-scale/1649
Sound will - more than likely - require machining the frame to squeeze in a speaker. So a drop-in sound install is highly unlikely for this unit. Even an HO Kato NW2 requires machining the frame just to convert it to DCC.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
What drop in decoder for kato RS2 Frame # 17843L N Scale