I was gonna ask why do you run the pipe under the floors and not just in the walls like electric wiring, but after thinking about it I figured must be impractical, to much work?
Since the leak is now known to be a pipe under the floor, the question seems to be how was it appearing where it was. First thought that comes to mind is where those pipes go thru the floor, both water and drain, there's gonna be a void there, it would be good practice I think to sleeve at least the water lines. Not the sewer pipes but the water lines maybe? that would leave a free path, but also do they run an expansion joint in your house slabs? that would be another breech thru the floor.
Maybe they just saw cut control joints to contain any stress relief cracking, that could be another source. Just picture that slab before the house was built there would be all kinds of thru slab paths for all the drains and pipes etc.
The odd thing is seems many of those paths thru the slab would be in the bath room and inside it's partition walls. water will always end up in the lowest point it has access to and since the bathroom floor would be the lowest point on the first floor, it should have water 3/8" deep, since that's the difference in elevation between the tile floor and the vinyl floor.
So what I'm thinking is it rules out the bathroom as the source of the water pushing up onto the floor but also even if it were coming up inside the walls where the pipes go through the slab, it should flow to the bathroom first or at least equally.
There's still some mystery, but I guess it wont matter as long as the pipe is fixed, I would lean to a conventional repair of the pipe, I know there will be alot of collateral hassles with jack hammering the floor up, but I think the insurance company would cover the additional cost. they are paying for the collateral damage now, which is gonna be more than the repair. doesn't make sense for them to save a little on the repair only to have to pay for future damage if that internal patch fails. Unless they plan on dumping you after they are finished with this claim, they do that some times.
As far as those manifolds go, I've only seen that once, an older house was completely re-plumbed and they used that plastic pex tubing and yeah it acts just like an electric distribution panel where all the different branches can be controlled from one point. And I don't know if I imagined this or someone told me, but I think there is actually an option of a way to protect those branches should a leak occur, almost like a circuit breaker where some kind of simple valve would close if it sensed an uncontrolled flow.
Sorry for the long post, I'm just trying to exercise my brain a little, I do basement waterproofing as well as other lines of restoration. This is normally a slow time, but this whole last half year has been really slow, so I've got to much time on my hands.
JB.