Well I cannot help you fully, but a little.
I recently auditioned the Polk LSi-15 briefly - one song but a good one - at a Frys Electronics, of all places. I don't know if they are nationwide, but we have several around here. The one where I listened has a dedicated sound room with doors to close off the thumping from the car stereo display... But another store has everything open, so you cannot tell a thing.
In any case, the LSi-15 are quite nice. The image was good and the sweet spot was fairly forgiving. In fact, you could wander about and not have terrible timbre changes. Frequency response seemed nicely balanced. It will really depend on what the placement will be in your brother's house because they do have the side-firing woofers. I bet they are crossed above 80Hz so might be directional. The LSi-9 (same thing less the low drivers and big cabinet) were also very good and got an excellent review in Soundstage. Probably not worth the 900 bucks due to lack of real bottom end, but the LSi-15 might be worth 1200. I would definitely have to do a home audition for that, and would want to have heard the M60s first, too. I only have M3s and like them a lot, so whadda I know how the bigger ones sound. But I did a long audition of the Audes Blues ($2000 and it looks just like the LSi-15) and think it is great. But lots of money.
Good luck, let us know if you get to do comparisons.
