My A3000UX came from the factory with *Multiple* sockets, and a ROM tower *that was not being used*. For some odd reason, C= put the unix booting ROMs in the alternate sockets, but shipped a ROM tower with the computer in case you wanted to use different ROMs (?)
If yours came from C= this way, maybe someone along the way lost the ROM tower?
Also, there are jumpers to select which ROM sockets you are using.
Mine even has a socket that works with A2000 ROMs!
Also, you mentioned your accelerator. You MUST change the motherboard jumpers if you remove OR add an accelerator. There are two that need to be changed, and what they are called depends on what rev your board is.