Tube amps that can hande 4 ohmsl

As can the Premier 12's. I have them driving Thiel CS6's

http://www.condor-connection.org/asog/tweaks/ps/zero/story.html

Hybrid amps may be another safe bet. I'm using a pair of Blue Circle BC2s (hybrid - 75wpc Class A, with one 6SN7 tube per amp) to drive my Audio Physic Virgos, and they seem to do a wonderful job. I believe the CEO of Blue Circle uses the same amps to drive a pair of Martin Logans (can't remember the model) that are notoriously difficult to drive.
Cheers,
John.

What is important is the output impedence of the amp....kind of.

If the amp has a low output impedence, like the Sonic Frontiers, the frequency response will be more likely to stay flat in the areas where you have an impedence dip.

If the amp has a higher output impedence, you can get a little bump there. That may mean a bass that is a little fat...which can be a positive anyway.

If it were just about measurements, we would all own Aragon. And marry a Stepford wife. My wife is a little quirky, but that is what makes it interesting.