While I have no experience with the KC62 it does at least seem to be more appropriate for LS50's than Ref 1's. But like most others here have expressed it's you that will have to let your ears be your guide. You definitely want 2 (at least) of whatever sub you go with, though. It'll be obvious why once you get them positioned correctly.
I have Focal Sopra 1's, a direct competitor to the Ref 1 and they also have better in-room bass response than the specs would indicate. But I already had and still use a pair of Rythmik G22 subs, turned down to about a quarter of their capacity. The sound is sublime and effortless. These are a sealed design, dual 12" driver (each) subs with DSP control and an 800 watt amp. I have mine mounted on Townshend Seismic Bars and can recommend them, too. The home theater guys don't care much for them because they were designed to be used in a music system (though if you demand more bass than these things are capable of producing then I have no interest in listening to your system). They produce tight, nuanced bass and won't break the budget, at least compared to upper end Kef subs or REL's. I think they complement the Sopras extremely well and even though I'm still considering moving to a floor-stander at some point I doubt very much that I will get rid of the subs.
