My Sonus Faber Amatis have weak bass even though I'm running ML 536s--800 w/ch into 4 ohms

One wall is windows. Floors are wood, but covered by a rug. Plenty of furniture in room. 

They sound great. They just have no bass. The second I turn on the KC 62s the sound is 10x better. I can't believe two $1500 subs make the sound that much better than the MLs and the SFs alone. I must be doing something wrong. 

Naim nd5 xs2

Nordost heimdall 2 rca

classe audio cp-800

Nordost Heimdall 2 xlr

mark levinson 536 monos

Nordost Heimdall 2 sp wire w Nordost jumpers

sonus faber Amati traditions

2x KEF KC62

AC - Tara labs and audio quest. 

It's like the whole system comes alive when the subs are added. I guess I just thought that with the Sonus Fabers and the ML 536s I wouldn't need subwoofers.

Living room 18x16x9

but room has two pillars on one side then a hall way. Which makes the room 18x19x9. And then open to kitchen with half wall. Which makes room 30x19x9. But one corner has a 45 degree corner for a fire place. 

Any way to upload photos?

Thanks all. I'll give it another try. I had 803d2s before. I thought they were to bass light. I moved up to the SFs hoping that would solve the problem. It didn't. I moved up to the MLs from a Classe CA-2200. The MLs have twice the power of the CA-2200. That didn't really make a difference on the low end. I've tried every cable possible. I've moved them around to every conceivable location in my room (which is somewhat limited by the fact that it's our living room, and I can only get away with so much with my wife. Thanks again.

BTW, not looking for crazy bass, but there is a completeness of sound that I get with the subs that I don't get without. The mids and upper frequencies also sound better with more fulsome bass. Not sure why, but that's what it is. I will say that the mids and hi frequencies are somewhat forward (not sibilant or harsh, just top heavy. But that could be because the bass is so weak). I listen to jazz and classical mostly. Bass drums, kick drums, double-basses, etc., are there but not there.

I guess as a side note--I usually buy used equipment because it let's me get things at a fraction of the cost that I would never be able to afford otherwise. The SFs and the MLs were both used demos from authorized dealers. With the SFs, the dealer was from out of state, so I didn't get the benefit of having someone come in and set them up. It has occurred to me that something is broken/wrong/malfunctioning, but given that the bass I am getting sounds good, my guess is that everything is working properly. It's not like the bass drivers aren't moving or producing sound. I just think there ought to be more of it.

@Audiotroy--never thought the room was that big, but you may be entirely right. I assumed it might have something to do with the fact that there is a half-wall between the living room and the kitchen. Maybe I just need the subs based on the size of the room.

@jl35--that may be it too. I really didn't expect to need subs. Or at least I was hoping that if I spent that much money I wouldn't need them.