I don't think any one $1k sub will do a lot to top two LFM-1 Plus subs. Besides that, then you get into mixing subs with different strengths, and that can become somewhat complicated to set up efficiently. It isn't impossible though.
One thing you might consider is placing the LFM subs near-field, like flanking your seating, and place the larger sub in the corner. Make sure the LFM subs are as equidistant from the listening position (or positions) as possible. This ought to let you run the larger subs closer to its potential without over-driving the LFM subs, and at the same time letting the LFM subs add a significant contribution.
There are a few recommended ways to set up multi-sub systems, you ought to look at the
Harman white papers on the subject as well as the
Geddes approach. You could also do a sort of two way sub system, as sometimes recommended by Hsu, where you have a sub dedicated to lower frequencies and then also have a mid-bass module. Whatever you do, you will need to make a lot of measurements to avoid cancellation, so make sure you have a SPL meter handy. To get the most out of multi sub setups, you will need to pay attention to phase, or else you can actually end up with less bass output than what you had before.
