GR Research has many planar loudspeaker owners (myself included) who have found musical happiness with any one of their subs. Look into the model F-12G, designed in collaboration with Danny Richie of GR Research (hence the "G" in the model designation).
If you are REALLY serious, and are up to a little DIY, the Rythmik/GR Research OB/Dipole Sub is THE sub for use with dipole loudspeakers. Details on the GRR website.
If you are REALLY serious, and are up to a little DIY, the Rythmik/GR Research OB/Dipole Sub is THE sub for use with dipole loudspeakers. Details on the GRR website.