You will need to determine which channels are dead for sure and which are operational 1st. You stated you had a bad nozzle check on your K & LK channels before sending it to be repaired (after doing 20+ cleaning cycles, which by the way is not healthy for your print and never recommended under any circumstances). Do determine which channels are actually functional you will need to get the air out of the lines, I recommend doing this with Flush carts and running Initial fills until you see flush on your nozzle checks. As I stated this may take more then 1 or 2 Initial Fills through the adjustment program to get the air out of the lines and the flush to the head, because of the amount of air in the lines at this point (and I am certain you have lots of air in those lines because the carts were run dry and the printer left to sit).
Here is a step by step for what I recommend:
1.Purchase a set of cartridges & enough flush to run 2-4 Initial Fills (approximately 30ml per Init Fills) 30MLx4 = 120 mls total keeping in mind you do NOT want to run these carts dry, so leave a bit of wiggle room, I would purchase 2x 700ml of flush
2.Fill cartridges with flush in equal amounts, reset cartridges to full (because the Initial Fill will not run if you do not)
3.Run Initial fill 2x for both sides (you will have to reset your chips for EACH init fill) KEEP AN EYE ON THE FLUID LEVELS
4.Manual Nozzle check to determine the results
5.If you don't see some of the channels returning, run 1 more Initial Fill
6.Manual Nozzle check-at this point you should have some channels printing fully with Piezoflush
7.If you still see some stubborn clogged channels, leave sitting for 24-48 hours and run another Nozzle Check
At this point you will have an idea as to which channels are dead and which ones are still operating, at which point you will be able to determine if you will be able to continue with color printing or switch over to Piezography. Also, you will know the state of the print head if you do decide to sell making it more valuable then if you were to sell it outright in it's current state. Chances are you will have a hard time finding someone to take it the way it stands with all the unknowns, so it is worth the investment of flushing to determine the condition of the head.
Hope this helps, Kelly