Sub or Subs to mate with Sonus Faber Amati Homage

What amps are you using? (or have used, since you said your have tried several)
I really think that might be the problem. Are you using tube amps? (Sometimes tube amps are a little weak on low frequency response.)
I would use either Krell or Levinson amps. (I use the Levinson No. 23 (200W/ch) on my Revel Studios and they are rated about the same as your Amatis are for frequency response, and I get pretty good bass out of them. Not thundering, but then again my room (16'x24') would sound boomy with too much bass.)

I believe that the Amatis go down to about 28 HZ, which really means that subs are probably not needed.

Those are my 2 cents worth anyway. Good luck.

PS I used to have a Velodyne (15") that had pretty good bass. The problem I always had with using subs was getting the crossover point right. Given your speakers, I think this might be problematic for you as well, since your speakers (theoretically anyway) have pretty deep bass response.

Well, while they are not Levinson or Krell, I think that the Classe amp you tried, should have provided decent enough bass.

Perhaps changing cables would help.
I changed from Tara Labs Space and Time cables to a MIT 770 CVT, (bi-wired) and I noticed a dramatic increase in bass on my old Sequel IIs, and the bass on my Revels is also good. You could give those a shot.

I hate to say it, but I think it might be your room, in which case that is difficult to correct. I think Rives might be the best person to turn to to solve this problem.

BTW, something I just thought of: What source are you using? I know that some digital (CD) players and quite a few analog sources are weak in their bass response. Perhaps you could try a different source and see if that helps.

Good Luck!