Tube amp for "difficult" speakers,,,

Since tube amps are more sensitive to overall load than most solid-state amps, it is better to know not only the speaker voltage sensitivity of 83 db/watt/meter, but the impedance load. A lot of speakers with low voltage sensitivity are relatively easy loads, so all you really need for a good tube amp match is a fair amount of output power. Conversely, you can have a 92 db sensitivity, but the load can have low impedance dips and can be reactive (high inductance and/or capacitance). In the latter case, it can significantly change the tonal balance of the speakers and/or cause the tube amp to run out of power, especially in the bass. You should be able to procure an impedance versus frequency curve for the speaker from the manufacturer, or you could ask them if they recommend tube amps. I seriously doubt any type of SET amp would work with these speakers, but perhaps some of the more powerful push-pull amps might.

your krell should be maximizing those dynaudios. just get a nightlight to see a glow. even a big mac with tubes isn't going to do any better.

Unless the speakers have a flat impedance curve no tube amp is going to do them justice for reasons mentioned above by Rlawry.

If you want a refined and liquid solid state sound, consider Pass Labs XA-.5 series amps.

If your speakers do present a difficult load, there is proabably no better all tube amp (hybrids would also work)to deal with dipping impedances the Music Reference RM9 Special Edition which is one of the few amps that actually increases power into 4 ohms (200 watts)compared with 8 ohms (160 watts) and that should be enough power to drive speakers with your sensitivity. However if I did have a difficult speaker load I would proabably look at the Pass XA.5 amps that Tvad recommends.

Increasing power to 200 watts into 4 ohms versus 160 watts into 8 ohms still causes a volume imbalance in the 4 ohm frequencies (they'll have less volume than the higher impedance frequencies). The speakers will sound tipped up with lack of body, IMO.

You need 320 watts into 4 ohms for 8 ohm speakers to produce a balanced sound from top to bottom.

The impedance curve is key. If it's relatively flat, you're in good shape to use a tube amp.