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

I agree with @audiotroy's analysis.  In the bass region, the speakers are "seeing" a huge airspace.

Also, eyeballing Stereophile's measurements from June 1999, the Amati is not a bass monster.  Its efficiency is on the high side, and (for a given enclosure size) there's a trade-off relationship between efficiency and bass extension, so "not being a bass monster" is no surprise here.

The slope of the Amati's low-end rolloff is fairly gradual, which to me implies that it might have been designed for fairly small rooms and/or placement close to the wall so that it would benefit from the resulting complementary rise in the bass region due to boundary reinforcement.

@torke, I suggest you enjoy how they sound with the subs and not worry about the fact that they "need" subs.  Imo that's just the nature of this particular beast in what is effectively a very large space at low frequencies.

Duke

speaker manufacturer

I don’t know if anyone is following this post any more, but i solved the problem and the bass is so much better. Finally what  was expecting, and I don’t even need the subs anymore. I just coupled the speakers to the floor instead of isolating them. Seems too easy to have worked, but it made 1000% difference. 

Glad you solved the problem. What were the isolating and coupling solutions you were using?

@torke Glad you we're able to solve your issues.  Which isolation footers did you have before and when you decided to couple them how did you do it?  Are the speakers on spikes now?  

There is another thread discussing footers and isolation here... https://forum.audiogon.com/discussions/footers-under-new-speakers

I made a comment about how isolation or vibration de-coupling may do more harm than good when it comes to bass weight and impact.  

It was a Herbie’s Audio product, which I’m sure is good for some  applications but the more research I did the more I realized I needed coupling, not isolation. I have hardwood floors glued to a concrete foundation. Anyway, the speakers are on the OEM spikes that are resting on 36 mm spike shoes that cost me about $90. Cheap fix; world of difference. What’s funny is that I was about to spend a mint on ISO-acoustic feet, which would not have solved the problem.