I like the suggestion that someone once made about borrowing a sub from a co-worker, friend, grandma or a neighbor and pair it with your Klipsch. If you split the LFE signal you'll have mono but you can see the advantage (or not) of having the two subs in your space, and the cost is about nothing but some time. If you are able to get the desired effect with two different subs I would imagine that a matching pair of high quality subs would do even more.
I have never heard the LFM but if it is like the rest of Outlaws products I'm sure it is a great piece of equipment for a very reasonable price, especially the pair price.
Like you I have a room with a large opening on one wall. The room is about 17x21x8 and I started with only one sub and I was never pleased no matter where I put the sub, it was either boomy to get the desired max volume or not loud enough when in a position that gave nice solid bass. Some might say that a better sub in the "solid bass" room position would be the best option but those locations in my room were unacceptable so I gave the dual subs a try and have never looked back. I also listen to DVD-A and I feel that is where the two subs shine the most.
Now if you have a friend with a "better" sub than the LFM then maybe you can try that as a single or again paired with your Klipsch.