Both male and female PC-mount BNC connectors exist. I don't know the manufacturer off the top of my head, but I do know I've got one in my parts box. I also have both male and female cables and do make use of them now and then, though obviously most equipment is standardized as you'd expect.
You can roll your own midpoint voltage reference, or consider the TI "rail splitter". They work well for opamp circuits, but power circuits are a bit harder. Does this amp need to go down to DC so it can handle offsets and very low frequencies?