Sub or Amp

Ok, wasn't sure where to ask this since it covers two areas, but since it's sound I'm looking for it ended up here.
I have a Kairn pre-amp mated to 2 Klout amps feeding a pair of B&W N802 speakers. My problem is I don't have enough bass.
My question is, should I look to get another Klout amp or a sub? Everyone says the 802's are enough you just need more power. The speakers are bi-wired so I could use one amp for the mid & upper on both speakers & an amp for each speakers lower end.
Or I could get a sub. But if I went this route how do I connect it to this pre-amp? It has no sub outlet?