Have you tried the Densen web site ? There's a chatboard where people discuss their systems.
I own a Densen B100 and it's a great amp, but as you say, it has a reputation for being a bit fussy. I have only heard the SF concerto, and not with the Densen (the amp was Quad) and I remember them not being bright, and having good bass for their size. I think the Densen can be bright with the wrong speakers, particularly metal tweeters, so I'd guess it could work quite well with your SF concertinos.
If you live in SF bay area you could bring your speakers over and try them on my amp if you're interested.
I own a Densen B100 and it's a great amp, but as you say, it has a reputation for being a bit fussy. I have only heard the SF concerto, and not with the Densen (the amp was Quad) and I remember them not being bright, and having good bass for their size. I think the Densen can be bright with the wrong speakers, particularly metal tweeters, so I'd guess it could work quite well with your SF concertinos.
If you live in SF bay area you could bring your speakers over and try them on my amp if you're interested.