Piano and Trumpet can sound bright

I played trombone in a ton of small groups and big bands - even large salsa bands. When a trumpet player wants to, he can burst your eardrum (although trombone can technically produce more volume, it's not as harsh). That being said, Miles can have a bright/brilliant tone, but it shouldn't hurt your ears if everything's right. The same should be said for piano. Even a guy like Michel Camilo who whacks the crap out of the keys doesn't sound harshly bright on his recordings.

Unsound,
I did say they could sound bright at times.I just deny hearing harsh and irritating which is different(at least to me).

I have the same cables (Kimber silver streak from CD to pre, PBJ from pre to power and 8TC speaker cables) ... the silver streak can be bright unless matched with a very high quality source. I have heard the same for the KCAG. I have a live room (hardwood floors, no heavy curtains, just an area rug, sofa and listening chair) so had the same problem with a brighter sound than I wanted. Moving the speakers further away from the sidewalls and toeing in them a little more to avoid the side wall reflection has solved the brightness. If that is not sufficient, try copper cables instead of silver. I am not familiar with your amp or speaker, but have heard very good comments on the Celestions as well as Quicksilver amps, so cannot provide any comments on these fronts.

In the vast majority of jazz clubs, the performers are miked. This is actually what creates most of the brightness, the sound systems are just too damn loud. There may be some clubs in NYC still that don't mike, but there sure aren't many anywhere else. That said, even with a performer that strives for a dark trumpet sound, which for instance most orchestral players do, it is still a bright instrument compared to most others. And most jazz trumpet players are not necessarily striving for a dark sound - a lead player in a dance band quite the opposite, for instance.

Check out the frequency response graph of the Celestion SL700 in this Stereophile review:

http://www.stereophile.com/content/celestion-sl700-loudspeaker-1991-measurements

While there is a big dip in the frequncies between 10k and 20k the spike beyond 20k would have to have an effect on the sound of the speaker,IMHO. That spike is found with many metal tweeters.