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

OP,

I think we are zeroing in on the problem. You are looking for crazy high bass.

B&W are know to be very bass heavy. And you you owned B&W803’s and did not think they had enough bass. So, what is going on here sounds like you want a very bass heavy system. If you want accuracy down to the bass and then a big kick, you are going to have to use subwoofers. and adjust them for the kick you are missing. Amati’s are made to sound natural and accurate down to around 28 hz or so and they sound that way,

I got rid of my subwoofers when I got my Amati Traditional. Don’t miss them at all, plenty of bass, Note, Sonus Faber makes three levels of subwoofers. That Gravitas are absolutely beautiful and match the Amati.

Alternatively you could go with the current top of the line B&W 800 speakers and massive MacIntosh monoblocks. These really rock and are very bass heavy. On the other hand MacIntosh is details / high frequency light... so the might create a problem for you.

I have a large and irregular room... 35' by 25' by 7'... highly irregular... they sound spectacular in my room. So, your room sounds good. Unless of course it is all tile, and windows and reflective surfaces. 

I own Sonus Faber Amati Traditional. There is no lack of bass or treble. I power them with ARC 160 amp in triode mode... so 70wpc. I seldom see them using more than a watt or two... sometimes ten at peaks. I can turn them up far beyond where I ever would want to listen and they are clear and non-compressed.

A couple things. I took off the little plate jumpers and put in high quality ones. I noticed a lack of bass once. I was going to reposition the speakers to improve bass, when I realized one of the jumpers have come off and one of the woofers was not working. I put it back on... bass deficiency went away.

Have you owned audiophile speakers before? Just wondering... audiophile speakers are designed to accurately reproduce the sound they are given... not to accentuate it... some speakers are designed to be very hot on top and overdo the bass. Just wondering about your expectations.

Just for fun I recently decided to completely redo my speaker placement. So I started with them a couple feet from the wall (the location that reinforces the bass) and worked them out until they were five feet out. I will say they really sounded great in all positions with only slightly more bass close to the wall. I ended up with them in the original position, about five feet out with no toe in... allowing them to disappear and cast a soundstage about eight feet back and beyond the speakers on each side., 

These are exceptionally natural, musical speakers which do not need enormous amounts of power to sound spectacular across the audio spectrum.

I guess we need more information from you. Your complete system with photos in your venue... create a virtual system in the area to do that... and we can probably help. Also, a little history of you and the music you like would br really helpful.