Saw that the board came with 3 connectors with space for 6 more. Does that mean I could just solder some more sockets onto it and it'll be able to handle 9 hashboards?
One would assume you could since people have been able to use the ones that did come with 9. With them selling IO boards now I would chances are just get one of them as it's the easiest fix considering your talking about soldering sockets.
Also know if you used 9 remember you also need larger cables. The standard cables would not be long enough to hook another S7 beside another.