Upgrading my SET amplifiers?


I am very happy with my Wright Sound 3.5/Lamhorn/Lowther EX 4 combo, but I know that the amps can be improved. I was looking for a Berning Siegfried, but nobody wants to sell this amp used and new is not longer available. I’ve read good things about Art Audio, Wavelength, Exemplar and the like, but I want to know from people who actually own those amplifiers or other very good SET amplifiers. I am willing to spend $ 3,000 / 4,000 in this upgrade. If possible, I prefer to buy used. Your help is greatly appreciated. Pablo.
pablovila
Instead of Lowthers I am planning to put my pair of Altec 755E's in a 2 cubic ft sealed cabinet. This should give good bass response down to about 40 hz and a sensitivity of about 103 db! A good match for my Sanei 2A3 SET!
755e you will get 100hz at about 94db in small sealed cabinet but your not going to listen and I know I am wasting my time 

Holy cow there is no way your going to get 40hz out of a pair of 755s!  Not even 15db down.