I don't know the TechnoArm, but the PH3 is a very good phono stage. I've directly compared it to the PH7 and found surprisingly little difference in performance with a Lyra Dorian (the PH3 seemed - maybe - a touch drier in treble). A better cart (or younger, more treble sensitive ears) might reveal more differences, but I'd guess that the equipment ahead of your PH3 is more limiting than the ARC phono stage.
That being said, I also agree with the sentiment that a phono stage (as well as a cartridge) usually has more "personality" than any reasonably good arm mated to a well matched cart. For that reason, I'd also expect that changing out the Benz cart in your TechnoArm will make a more pronounced difference than changing the arm itself. And, of course, "more pronounced difference" does not necessarily mean you'll prefer it.
Your choice should also anticipate any future upgrade plans you may have. Since you mention that you might add a second cart, consider that several phono stages offer more flexibility than your PH3 in optimizing the "environment" (load, gain, etc) for whichever cart you might choose in the future.
BTW, I currently own a Rhea (great flexibility - load, gain, multi in/outs, bal s/e, etc.) and, personally, prefer it to either ARC unit - in my system. It's a rounder, somewhat more classically "tubey" alternative to the more neutral sound I heard from both ARC phono stages. For context, the Rhea sounded more neutral to me than the EAR phono stage I also auditioned. I feel that Aesthetix found a nice spot on the continuum. IMHO, employing all ARC electronics ahead of Cremonas may diminish the basic character of the speakers in a way that many might prefer (more neutral) but didn't work for me (drier). YMMV.
Caveat: If you're thinking of a used Rhea, know that early production units (like mine) could be noisy. A few years ago, Aesthetix modded mine to match (then) current production and this problem was eliminated.
Since I also have used both the Rhea and the PH3 with ARC amplification (LS25 and VT130SE) and Cremonas, I can tell you that you will hear a definite change in "flavor" if you go to the Rhea from the PH3. I can't tell you if you'll prefer it, only that I did.
Marty
That being said, I also agree with the sentiment that a phono stage (as well as a cartridge) usually has more "personality" than any reasonably good arm mated to a well matched cart. For that reason, I'd also expect that changing out the Benz cart in your TechnoArm will make a more pronounced difference than changing the arm itself. And, of course, "more pronounced difference" does not necessarily mean you'll prefer it.
Your choice should also anticipate any future upgrade plans you may have. Since you mention that you might add a second cart, consider that several phono stages offer more flexibility than your PH3 in optimizing the "environment" (load, gain, etc) for whichever cart you might choose in the future.
BTW, I currently own a Rhea (great flexibility - load, gain, multi in/outs, bal s/e, etc.) and, personally, prefer it to either ARC unit - in my system. It's a rounder, somewhat more classically "tubey" alternative to the more neutral sound I heard from both ARC phono stages. For context, the Rhea sounded more neutral to me than the EAR phono stage I also auditioned. I feel that Aesthetix found a nice spot on the continuum. IMHO, employing all ARC electronics ahead of Cremonas may diminish the basic character of the speakers in a way that many might prefer (more neutral) but didn't work for me (drier). YMMV.
Caveat: If you're thinking of a used Rhea, know that early production units (like mine) could be noisy. A few years ago, Aesthetix modded mine to match (then) current production and this problem was eliminated.
Since I also have used both the Rhea and the PH3 with ARC amplification (LS25 and VT130SE) and Cremonas, I can tell you that you will hear a definite change in "flavor" if you go to the Rhea from the PH3. I can't tell you if you'll prefer it, only that I did.
Marty