I think I hit every nail on the head with this install but this one. Easy fix. I'll try to locate a route under the floor for the HU power as you said. I'm going to opt out of the relay and just fix the problem as David suggested. Probably leave the rca's where they are.
I have all the amps run like you mentioned in your post. You can see the blocks and we made sure they were all the same length from that. But never thought about the source.
When I was a child, I used to talk as a child, think as a child, reason as a child; when I became a man, I put aside childish things.
1 Corinthians Chapter 13 - 11