So you want to get rid of the current headunit ( which I assume you bought second hand since the 9100 is a japenese version ) for the 8750? negotiate the price if you want that particular headunit.
You have pioneer components front and back. Have you considered where you are placing the rear tweeters?
A busted coil on a sub is repairable. But unless it's done professionally, consider it junk. It will keep giving you issues in the future so why not upgrade the sub too? And 5k for a coil change on a 10+ year old sub is absured
You actually spent 12k on repairing an amp? What was done to it? alien technology infusion? If your amp needs to pushed that hard to get the sub going, the amp is a goner and underpowered. you would need atleast 150-200rms to run a 400rms sub. ~300rms is what most 4 channel amps will do on bridged and thats best you can get out of them considering you have 12V+
Kicx audio is another generic chinese brand that write big numbers like 2000watts on their amps when they can only push about 100-150 on bridged. I'd suggest to get a good branded ( even if they are older gens ) 4 channel amp for the speakers and a mono or 2 channel for the sub
i'd suggest to gather these things. When you have everything, do the install
