VX included one i860 processor with a 32-bit VRAM frame buffer (plus an 8-bit GX frame buffer) - see the brochure below for a block diagram.
MVX added a board with 4 more i860's (potentially up to 4 boards with 16 processors)
Inter-processor communications was via dual-port VRAMs with the VRAM port
used for high-speed block transfers.
Multi-processor control was via a message-passing system for the i860 processors that could also include the host workstation's SPARC processor as well as networked processors. See "A visualization programming environment for multicomputers" by Gary Bishop, Mark Monger, and Paul Ramsey.
Functioning systems were built and software ported, but unfortunately Sun never released them as products