Hey Vicky,
Just to understand your setup:
The Blackmagic Intensity Pro 4K is either HDMI, 2 Channel RCA HiFi audio in 24-bit (or SPDIF Audio to which there are little information about). But there is no SDI?
Your Genelec 8010 speakers are XLR in?
Cheapest, not necessarily perfect, is to to get a mini jack stereo to 2 x XLR male (Left and Right) and use the audio out of your headphone socket. You will still need to use the software volume control on your Mac/PC. Or if you have the multicore cable, get two phono to XLR cables.
The alternative is a break-out box, and once you start spending money on that, you might end up with an Avid S1 or similar. There is likely to be other motorized Audio mixers on Black Friday sale, but would not know where to start, and how it will integrate into your system.
Hope that this helps just a little bit.
Atb
Mads