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

@torke 

I was just reading about your amps and I have another question or six.  What are they plugged into? Are they sharing the same circuit? Is it a 15 or a 20 amp circuit? Are you using a power conditioner? Are you using the stock power cords?

All the best.

May I respectfully suggest our Caldera 10 sub from Vera-Fi

I realize no links allowed - but this sub has won multiple Product of the Year awards even at $199 each 
 

Please give it a look

Best wishes - Mark 

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