Benchmark AHB2 compared to Rogue Atlas Magnum III

Very different amps indeed, and I’m sure your excellent speakers will easily reveal the differences.  It completely depends on what improvements/sound characteristics you’re after.  What amp are you using now?  The Rogue will add a little — though not too much — tube warmth and tonal color/richness whereas the Benchmark will give you a similar sonic signature of your DAC, that being very detailed and neutral.  Your call.

It's not just a matter of the speaker being good enough to reveal differences. It will have a lot to do with the impedance of the speaker at various frequencies, causing the tube amp to produce a slightly different frequency response. A good speaker with stable impedance will sound more similar between the two. A good speaker with bigger peaks and dips in impedance will be more revealing of their differences.

The only way to know for sure if you'll like one better than the other with your F208s is to give them both a try. 

Absolutely they will sound different largely due to output impedance difference as per @asctim and the difference in distortion. The only way to know which you prefer is to listen and compare.

Difference is between virtually no distortion and able to drive anything, vs the often preferred distortions, not well quantified, from tube amplifiers. 

Just my impression, but tubes seem to be more dynamic for the power. Amps like the Benchmark somehow seem a bit stiff upper lip if you get what I mean. Could be I am so used to MOSFET amps. 

Another impression, the metal domes in Revel's ( listened to bookshelf's only) just get to me slightly from otherwise very well balanced speakers. Guess I am just a soft dome guy. ( leaning to either my own or Sonas Faber) 

Only way to make the choice is compare them both side by side. Listening one by one does not tell you much. Our memory is not that good and out subconscious bias is stronger. You will hear what you want to hear and it does not matter what you think you want to hear. 

IMHO, there is no such thing as a good speaker with stable impedance.  Some better than others, some horrible, and yes it effects the sound of an amplifier.  The better the amp, the more load invariant it will be.  I expect the Benchmark to be immune, where a Fosi V3 is a disaster.  Really ugly impedance/phase can actually cause an amp to be unstable if the feedback compensation was not well enough done. Boy to I know about his. $$

As I have improved my speakers, DACs, amps, I am in a quandary. Really good recordings sound better, but poor ones sound worse. Makes me wonder if the distortions and masking of tubes, maybe preamp, would help the overall musicality. Most of my music is "my generation" so early remasters of tape or first generation digital, so not very good.