Benchmark AHB2 compared to Rogue Atlas Magnum III

Very different amps.  Paired with Revels F208, and a Benchmark DAC3, do you thing there will be a difference in the sound?  I am unsure if the F208's can reveal the differences.  If there were to be a difference with these speakers or an upgraded speaker, what might the differences sound like, or maybe not much difference between two great amps?  Thanks.  I have never owned a tube amp.  I have listened to this Rogue amp on different speakers though.  


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.