Water Sensor Power and Wiring

jmistler said:
How about exporting the power source for those 8 GRI-2600 zones + 4 PIRs out to an Altronix AL400ULXPD16? That would free up space inside the Elk enclosure, provide fuse protection on the sensors, and provide additional aux power for any Elk boards like the M1TWA, etc. Am I thinking correctly there?
One issue that comes to mind (given my inexperience with wiring) is how to physically separate the green+yellow pairs going to the M1XIN from the red+black pairs going out to the Altronix, since they are bundled together in the 4-wire jacket from each sensor zone.  I'm sure that's a stupid question to anyone else on this forum, but hoped I could get a little guidance.
Using the AL400 to provide power to the GRI-2600s and PIRs is a reasonable way to do things. 
If the AL400 is close by to the M1 enclosure, it's easy to connect them together with a short length of PVC conduit.  That'll protect the wires running between them.
Bring the sensor cables into the M1, and allow a few extra feet of cable once it enters the M1 enclosure.  Experiment with a length of dummy cable first, before you run all the real ones,  so you have a good idea of how much slack to allow.  It's easy to use up a foot or more running the wires in a neat fashion around one enclosure and then over to the other.
Strip the outer sheath off of each cable, and run the yellow and green wires over to the zone inputs.  Allow a few extra inches of slack so you can move them from one zone to another later, if the need arises.
Then run the red and black wires through the conduit to the AL400 and connect them up to the PD board. 
Below is a diagram I created a while back when a similar question came up.  It shows some bundling of the power wires in the M1, and then a smaller number of long pigtail wires running through the conduit to the PD board.  Depending on how many wires need to connect to each fused output, you will need to do this somewhere.  You could choose to just run all the power wires to the AL400 and bundle them up once they get there.  That will put the wire nuts over in the AL400 and leave a little more space in the M1. 
Just as an aside, have you looked at photos in the M1 Hall of Fame?  There are quite a few installs there, some simple and some very elaborate.  It's a nice reference on how you can go about arranging things.   When you get to the bottom of the first set of pictures, keep scrolling to see more.
Here's one photo where they used an Elk PD9 (it's in the lower middle with all the LEDs).  The aux power looks like it is coming from VAUX rather than an aux supply.  
Here's another Hall of Fame photo that also shows a PD9 board.
In the After picture, the upper can has an Elk P212S aux power supply right above the battery, and the PD9 board above that.  The M1 and a bunch of input expanders are in the larger, lower can.
It looks like they chose to bring all the cables in through the top can.  There's so much wiring there, it's hard to tell what is powered by the aux supply.  Some of the cables just pass through to the lower can.