If I recall correctly the original video toaster, and I believe even the revised toaster 2000 and 4000 all occupied the video slot, a dedicated internal interface that provided direct access to analog RGB component signals as well as some other video timing and audio channels. There was no connection to the Zoro II or later Zorro III system buses. The Amiga 4000 video slot added digital rgb counterparts to these analog signals, and also some oddball 8 bit connections to,I believe the parallel port UART pins.