bnc splitter box and chroma luma question

[trydowave]

hi all. since one of my 1084s started to die the other day i want to get all my machines running to my sony bvm 20e1e via bnc. Right now i only have one bnc card with vsync and that allows me to plug my pc via vga to it. i have an amiga 500 on the other bnc connection with no vsync (the amiga is the only thing i can get to work without a vsync connection and i still dont know why?) anyway. I would like to swap out the pcs vga to bnc for a bnc to bnc and then get a bnc splitter box. one end connected to the bvm and the other connected to multiple devices. for example the amiga and my speccy through rgb scart to bnc and then theres the c64s. will i be able to connect the c64 via a luma/chroma or svideo cable to bnc. Would that work? and if so does anyone know where to get such a cable and the bnc splitter/switcher box? phew... anyway. thanks. in advance for any advice