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

@torke - need more info

1. What’s your audio chain electronics+speakers
2. What’s the size of your room WxDXH?

Do you have other amp ? If you do try it. Maybe something is wrong with the amp not speakers or speakers placement.

Do you use Roon? The DSP should fix it unless there is something like a bass driver or drivers not working right.  
 

Making sure everything is wired properly to be in phase is important as mentioned.  
 

Roon DSP can invert phase as needed so easy to a/b compare. 

Are these speakers new?  How many hours do you have on them?  Sounds like they’re not broken in yet or as others mentioned maybe wired out of phase.  Did you get these new from a dealer?

The first thing I would check is to make sure they are not wired out of phase and it could be possible they are wired out of phase internally.

Ok so you have two threads one on the highs and one on the bass. What's your room and setup like? And are you sure you have your speakers wired up correctly?