The dbh instructions tell you how to do this. But you lose 2 spots. Also keep in mind that your wire run length is the sum of all devices plugged in to the dbh times 2. With 14 runs, it could be too long. So you might instead choose to run the two dbh's in parallel directly off the Elk. Of course this means that everything else will have to run off the dbh, since the Elk can only have 2 parallel runs.
Lastly, it doesn't sound like you have considered grounding and lightening protection. Running wire between structures underground is a risky thing. Are you putting in a separate electric service in the second building? If so, you need to make sure you only have a single ground for both structures. In other words, don't use a grounding spike for building 2, tie it in to building 1's ground. A lightening strike will setup a potential in the earth and typically this will weaken as the distance from the strike point increases. So the closer ground will have a different potential than the further one, and a current will try to run between them if there is a path. Since you have Elk stuff grounded in the one building, and other stuff grounded in your primary building, it very easily could use the communications cabling between the two close that potential difference. The basic jist is, you want the potential throughout your entire interconnected stuff to rise evenly together and fall evenly together. Think of a wave of water, you don't want two boats tied together scraping sides when the wave lifts them sequentially, you want a single boat that lifts and falls as one.
Also, the wires under ground should be shielded and grounded to prevent EM induced current in the wires. The grounding should be to the primary buildings ground, the same ground that everything else is attached to..
