Tube amp for "difficult" speakers,,,

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.

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.

The OP's speakers have an 83dB sensitivity.

The amp's power, or the size of it's transformer is not really the issue. It's the impedance curve of the speakers that matters.

I owned 160wpc VAC amps, which I tried on my Silverline speakers which employ Dynaudio drivers. The Silverlines do not have a flat impedance curve, and the result was an aggressive, tipped-up sound without midrange weight or sufficient low end to balance the highs.

Your VAC amps are considerably better than were mine, and they use 300B tubes, which have the characteristics you describe. Do you know the impedance specs of your speakers: lowest, highest and nominal? That'd be helpful for anyone reading this thread.

The impedance specs you post above are pretty favorable for a push-pull tube amp running on 4 ohm taps, IMO, since the peaks and dips are relatively flat.

So, I think the recommendations above would be good possibilities...namely VAC and Music Reference.

I have owned a couple of VAC amps including the VAC Phi 110/110, which was stunning. I have heard the VAC 30/30 Signature, which was also magical on a pair of Merlin speakers (although you'd need the extra power of the VAC 70/70).

Have fun!

Which amps mentioned would you not recommend and why? I'm interested to learn the reasoning.

It's not a question of having enough power to drive the Dynaudios to a proper level, it's a question of frequency balance. Since the Dynaudios dip to 5 ohms in the bass region, and have an 8 ohm nominal rating, I believe it's probable the bass will have less volume than the highs, and therefore the speakers may sounded "tipped up", although it won't be the fault of either the speakers or the amp, but rather the result of a speaker/amp mismatch.

Chapter 15 of Robert Harley's book "The Complete Guide to High End Audio" has a good explanation.