what speaker for rega brio-r

The LSA .5 pairs well. I also had a pair of Triangle Titus ES's when I had a Brio-R that sounded quite nice.

Stay with the REGA speakers for that special "je ne sais quoi" REGA synergy.

REGA R3/RS3s are perfect. ~ $700 used (and no stands required) . You can get the RS1s brand new in that budget range but you will also need quality speaker stands for them.

(I've had the R1s in a prior "B" system and I currently have the R3s as rears in my HT)

The R3s/RS3s are quite the Goliath killer. Either can be put close to the wall for speaker placement.

Give them an audition

I don't know about the LSA .5, but I just auditioned it with the LSA Statement, and it DIDN'T make the most of that speaker's abilities. It did a better job with the Silverline Prelude. I haven't compared the Prelude with other speakers, but it sounds pretty good. I'd like to hear more first hand experiences with the Brio-R.

Vandersteen 1CI
works great
Test with Johnny Cash and you should hear the advantage
a multi enclosure makes over a box.
JohnnyR Vandersteen dealer.

My office system is comprised of a Brio-r driving a pair of Ascend Acoustics Sierra-1 monitors. Anti-cables interconnects and speaker cables. For a 10+ hour work day it is a very good and non-fatiguing combination.