Rega Brio-R Break-in time.

Ok, good, since you answered first....I know nothing of your speakers. What do some/many use to drive them? Perhaps the Brio-r is just not the right amp?
And the Tellurium cables, which are designed by a guy who supposedly helped on the Naim cables...how do you know they work with Rega? Did you try any other cables? etc? I'm not trying to be argumentative in the least....just to ask why you thought the Brio might work in your situation. Nor do I really feel the need to defend it. I've heard it in some great sounding systems. The above posts also confuse me entirely....I think they're doing what you have done and inserted it into systems it wasn't meant for. Perhaps.....

About the Tellerium Q cables, they have nothing to do with the NACA5, its just that many Naim people are using them, simply because they are British based and getting some press over there. The Tellurium Black has a consistant sound across 3 different amplifiers I have played with recently, and they are not tone controls thats for sure.

The Cirrus speaker is ultra resolving and revealing of equipment, cables and power related issues. I do not think the Brio-R has trouble driving this speaker. Quite the opposite, I think the Brio-R can drive much harder and easier than 3 other amps at 70 watts and another at 100 watts.

But this is what I hear, voices are a bit colored and not neutral, strings on guitar do not sound real and there is a lack of ambient detail, but it all sounds great, like there is an additive effect of tonality.
Maybe it all opens up with some break-in, I will perhaps just buy one to really see.

JMTCW. I've compared the Rega Brio R with Brio 3, its immediate predecessor, side by side, over an extended period, say 50 hours. I am very familiar with the Rega family sound (having spent over 30 years in audio). The Brio R sonic character is vastly different from the Brio 3. I concur with mezzanine and others who are concerned with the Brio R displaying metallic harshness in the upper-mids and treble. I also feel its overall presentation is sterile, distant, spatially-constrained and lacking air/bloom in comparison to my references (Canary tube pre-amp, Atoll FET power amp, fed by Oppo 93 and custom DAC, powering Merlin TSM monitors, Huffman ICs and Clear Day speaker cables). In examining the Brio R's pre-amp section Rega appear to have installed an ancient TI TL072 opamp on line-level duties with what appear to be cheap Arcotronics(?) polyester 2.2uf input coupling caps. These components differ from the Brio 3 which appears to use a JRC opamp and Evox MMK input caps. These two aspects are likely to shape both amps' sonic characters significantly. I do hope Rega designers at least consider modifying the Brio R's front end for enhanced musicality. To be fair the Brio R's power amp section does a great job of delivering dynamics, grip, extension and PRaT. But this prowess cannot entirely compensate for that other perceived sonic shortcoming. Unfortunately it makes the Brio R tiresome to listen to, and does not quite fullfill its undoubted potential. YMMV. Enjoy the music!

I'm considering the Rega Brio-R for my Vienna Acoustics Mozarts (90db, 4ohm), would it be a good match?

IMHO Vienna Acoustics Mozart Grand's are highly musical speakers that are finely balanced. Electrically the Brio R would suit, given its claimed load stability down to 1.7 ohms. The rest of your system's synergy is important, including source components and cabling. See my earlier comments as to Brio R sonic character.