Robert, you will not get very much bass out of a SET unless your speakers are extraordinarily SET friendly. If bass is more important to you than the midrange and top end offered by SET's, then I would suggest you look elsewhere.
I have owned the Cary CAD-805AE, and it is definitely made in the USA. The fun thing about this amp is that it is tweakable - both 845 and 211 tubes are supplied. You can also choose between 0 and -10dB negative feedback (but once you try the NFB, you will want to leave it at 0dB). The 845 provides a gorgeous SET sound - the trademark clarity and liquid midrange, and has a lovely full and warm sound. The 211 is slightly less SET-like - it has better control of the bass, but the midrange and top end become more etched. Neither tube handles the bass adequately - bass is insufficient and flabby.
I have never had an opportunity to hear the Atma-Sphere or de Havilland amps, so I can not help you there.