MoFi Sourcepoint 8 or Q Acoustice Concept 50s

With your current amp and, I assume, you are keeping the Rhythmik 12"Sub, the SP-8 would be my choice.  I like the Mofi speakers I've heard.

If tube amp DF goes down to 2, meaning its output impedance is as high as 4 ohm.  The perceived increase in loudness is going to be 26% in high frequency.  You need attenuator to tame it down or avoid using such tube amp on speaker with char. imp. of this behavior.  

@lanx0003 @dynamiclinearity - Thank you for your insights and guidance.  The Aragon Amp has a Damping Factor of greater than 500 according to the original Stereophile review.  It is dual mono (designed by Dan D'Agostinto) who designed the Krell amps and provides very high current and will play near 800w into 2 ohms.  Another consideration - for the 8s - is that i can actually place the acoustic center at or a little above ear height which puts the top of the speaker at 45 to 47 inches.  I am 6'-2".  I can point them into the room rather than directly at my listening position - attenuating any treble brightness .  As for casual listening, they are high up enough to play over some very low slung mid century modern chairs that I move when it is just me listening.

You need to listen to both speakers, not to see which is best but which one you prefer. Both speakers are designed by two of the best designers in the audio world today.

I like the Mofis but will stick with Ohm Walsh.   BE sure to check and get assurance of a delivery time these days with Ohm however, they are navigating a major change in ownership and mgmt over the last year or so and I read some reports of customers having issues that were never a problem prior.  Hopefully teh smoke clears.....still the best value for music lovers in my mind!.