Well I do not believe you will need the Elan Sub. I would approach the intergration of the second ULS by leaving the first one where it is now presently located.
First, you would go through the process of gain matching the two ULS-15s. The first one has already be done, so place the new one in the same location you place the first one, when we did this process a couple of weeks ago, and adjust the gain on the new one, using your SPL meter at the same place you had it when you measured the first one so it also is playing the same dB as the first one.
Now using the wireless feature on the second new ULS, BTW congrats, I would place it first by the fireplace and play some heavy bass content, walk around the room and see how it sounds, again listening for the tightest smoothest bass. Then repostition the sub to the corner where the Elan is and again listen and see if there is an improvement. We also talked about co-locating both subs below the TV so this would be a third option to placement in your room. So bottom line you have some work to do next weekend, or sometimes, you can spread out this process over several weekends. IOW place the second one by the fireplace watch some movies and listen to some music. Then the second weekend move it to the right rear corner and so on.
But as you know everytime you repostition the subs you will need to run Audyssey, one pass so that you can check sub trim level in the AVR followed by the complete 8 pass calibration. So this can become time intensive because you also might have to adjust the gains on the subs volume knob when you combine the output from the DD system.
Once you have determined what sounds the best in your room you can then plan out how to hardwire the second one and remove the wireless sender.
I really do not anticipate you needing to mess with the phase switch on the ULS-15. Leave both at 0. Then what you would do is play with the distance setting for the subs in your AVR. If Audyssey sets the distance at say 10 feet, adjust the lenght so it reads farther away, say 12 feet, play an 80 hz test tone (if that is the crossover frequency you have chosen in the AVR) from your BD player using the supplied CD from HSU. What you are listening for is a greater output from the subs at the LP. You can even use your SPL meter for this process. Play the 80 hz note at the distance that Audyssey automatically had setup then lengthen the distance and replay the 80 hz note.
Am I making any sense to you about the phase? What we are trying to achieve is the subs cone movement is playing in sync with your main L/R speakers.
And as you know you can always call me for further help. Of course you really should pay the first invoice I sent you.