DeVore makes some very nice, not at all harsh, floorstanders that are more cat-friendly than the Vandersteens. Their speakers sound very good and are relatively easy to drive.
Although not necessarily in the "mellow" and warm camp, I like speakers made by Neat because they don't have the brittle edginess and sibilance that is quite common in high end speakers these days. They are also a pretty good bargain price-wise and should also be cat-friendly.

