[Rameish]

Okay, I'm not computer savvy. But i do wish to get the best sound out of my Mid 2010 iMac 27 inch with Graphics Card: ATI Radeon HD 5759 with 1024MB ram.
 
Intend to hook up to my IMac:
Option 1: via optical cable to TC Electronic BMC-2 then to a pair of Genelec 8010
Option 2: via 1/8inch (out of the headphone out on the iMac) to XLR on the Genelec 8010
Option 3: via a DAC like Schiit Audio Gungnir DAC the XLR to the Genelec 8010
Option 4: optical cable to TC Electronic BMC-2 then to a pair of Dynaudio BM5 mk iii via XLR
Option 5 : USB from iMac to Resolutio Audio Cantata then XLR to either Genelec or Dynaudio BM5 mk iii

 

[ProtegeManiac]

I'd go with 1 & 4, that way you just set the gain on the amp mounted on each speaker, then use the BMC-2's volume control as master volume. Just check and make sure it also affects the monitor outputs.

 

[RonaldDumsfeld]

None of the above.
 
The most important component by far is the loadspeakers you chose to buy. Genelec and Dynaudio make professional grade products. You should buy a USB capable monitor controller or audio interface designed to work with such active monitors. USB is technically superior to S/PDIF, much more versatile and future proof. You will want to connect sources that do not have optical at some point. Make sure you get something with it's own power supply, then you can use it when your computer is not available. Extra inputs and outputs will prove to be more useful than you currently realise. You could add a BT or wi-fi dongle (for phone or tablet for e.g.) or analogue source such as a TT microphone. Extra outputs are useful for cueing, adding zones or fills or simply to listen to music on your speakers while you use a headset to play games or Skype. The more expensive units have better software, better long term support and last longer so save money in the long term.
 
Good entry level examples are the Focusrite 6i6, Native Instruments Audio 6 or the Audient iD14.
 
For closer to your budget you could get a MOTU Audio Express, Audient iD22 or SPL Crimson.
 
Exceptional examples for a little more would include the RME Babyface and  MOTU Ultralite. Great software in both.