At the risk of offending my fellow members, if you run two JL subs and they are set up correctly (emphasis here), one for each speaker, there is aboslutely nothing inherently wrong with combining them with a full range high performance speaker for music playback. You will not only give the music more foundation, but you will also deepen and widen the soundstage, one of the often overlooked benefits of adding two subs to your system.
In addition, running two JL subs will tend to minimize the difficulties you can encounter with room integration when running a single sub. It's my experience that people say that adding two subs is one of the single most satisfying music system upgrades they have made.
Since you already have the subs, it costs you nothing to try. Just remember that how you set them up can make or break the sound.