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. 

@tvrgeek

My impression of these really well controlled, ultra low distortion amps is similar to yours. Stiff upper lipped is a great description. I’ve used the word "dry" in an attempt at a description of the effect, but they seem to have an iron fist on the speaker, minimizing its ability to express some character in its relationship to the amp. I’m sure it’s technically correct. I do like that sound in some ways but I think I’d need to design a speaker and setup a room around that as a starting point. The upside potential I’d bet is ultimately higher.

No really good speakers with stable impedance? Can you elaborate on that further?

And yes! There is a struggle between perfection that brings out the best in the best recordings vs. a forgiving sloppiness that doesn’t fully reveal the best but is graceful with less than the best. What to do? It’d be nice if you could just flip a switch or turn a knob on your system to go from exacting to more forgiving. With my active crossovers and EQ I can sort of do that. I’ve found that a really flat and extended response sounds great with some good recordings, but on most stuff sounds too edgy and bright. I need more downward slope in the treble to get a forgiving but less airy and spacious sound. Also a tighter directivity with less room reflection is fantastic on some recordings, where others need some room reverb to soften, blur and sort of fatten up the sound. I think there’s more to it than just bad and good recordings, but different kind of recordings needing a different playback to sound their best.

About metal domes, I don’t have a clear opinion on it due to a lack of much experience, but so far my favorite speakers that didn’t use compression drivers had soft dome tweeters. What always amazes me about a soft dome doped silk tweeter is that it can make such detailed, shimmery metallic sounds when they’re in the recording. It’s hard to get my mind around how a slightly rubbery, tacky, soft thing can sound like that.