I've owned both Thiel 2.4s w/MCS-1 center, and LR3s w/CC3b center. Both are very good, and essentially you've identified the main difference. I never had a problem with fatigue setting in with the Thiels, however system matching is more problematic and prone to sounding thin or bright if not matched properly. Generally this is more expensive to achieve with Thiels. I do think the Aerials have an advantage in timbre matching, seamlessness of the front stage, and the ability to play louder without strain during bombastic scenes. The Thiels are fine, and can handle a fair amount of power, but their smaller drivers w/1st order xovrs sound less relaxed when the going gets very demanding. Both need solid power. The Thiels need refined power, whereas the Aerials need an amp that is of good quality, but is a little more crystalline in nature, and has good slam. In either case you will need a good sub since you should be high passing both alternatives at 80hz. For music I prefer the Thiels overall, just more potential imo for 2 channel stereo.
Aerial 7B vs. Thiel 2.4
I am building a HT system and am wondering what other Audiogoner's think about building a HT system around the Aerial products (7b. CC3b and LR3's) or a Thiel system (2.4 as mains, MCS, and 1.6s). I think the Thiels are extremely revealing whereas the Aerials tend to be a bit more mellow. I will most likely be using Krell Showcase as the pre/power combination. Thanks.