Without knowing more, I'd suspect that the B&K amp you auditioned is not functioning properly, and needs repair, or perhaps there is a propblem with the speaker cables you are using. There are some amp / speaker cable / speaker combinations that cause oscillation in the power amp, which may be heard at a bright, ragged edge to the sound. There was a lengthy thread here on A-gon about 6 weeks ago about Alpha-Core Goertz speaker cable sometimes causing amplifier oscillation. If the oscillation is severe, the amp will overheat and may even shut down. Does the B&K amp overheat? If so, it may be oscillating.
Most of the B&K amps I've heard over the years have a smooth, relatively mellow sound, not bright as you describe. I think the B&K 1430 is the 3-channel version of the 1400, which is a decent sounding amp. In this situation, I'd be inclined to suspect the particular amp is the culprit, and not the B&K "sound" as a brand. If anything, the B&K "sound" tends toward a bit of warmth in the mid-range, and slightly rolled off in the lowest and highest frequencies.
Most of the B&K amps I've heard over the years have a smooth, relatively mellow sound, not bright as you describe. I think the B&K 1430 is the 3-channel version of the 1400, which is a decent sounding amp. In this situation, I'd be inclined to suspect the particular amp is the culprit, and not the B&K "sound" as a brand. If anything, the B&K "sound" tends toward a bit of warmth in the mid-range, and slightly rolled off in the lowest and highest frequencies.