if you like them, they sound good to you, and they are functionally sound, our opinions are worthless.
my experience has been that yamaha has better consistent quality control, but it's hard to beat a well made bach 42. but when they suck, they really suck. quality control has been questionable over the last so many years.
but the fact is, you'll get as many answers are there are players. at the end of the day, you'll sound like you on whatever horn you play. i play a king, a conn, two bachs, and was playing on a yamaha .525 from time to time. all great horns man. if it ain't broke don't fix it!
Well, the reason the Wind Symphony plays the Yamaha's, is because its a matching set of 6. They want all the horns to be identical. So its sort of like down grading on the horn, which is what im worried about. But is it downgrading at all? Im just not sure of the quality of yamaha horns.
I wouldn't say a yamaha is any better or worse.. it's just different. whether that difference is something you can deal with is entirely up to you. some great pro players play yamahas. ultimately, what you sound like has more to do with you than the horn. besides, you can put six guys on the same darn horn who have no concept of sound blending and they won't blend. get six guys on different horns who know how to blend into a section and you'll get a better result.
heck, the only time i play the horns my work gives me to play is when i'm fearful for their safety .. (which then, i certainly wouldn't use my own personal equipment). otherwise, i play my own horns even though i am supplied others to play on.
Well, it sounds like your teacher doesn't know any better if he/she wants the horns to match. Case in point: The Boston Symphony trombone section has one Edwards, one Shires, and one Yamaha. And guess what? They sound fantastic.
Also, I play in a jazz trombone quintet. We have a 1930's Conn, a 1960's Conn 6H, a Lawler, a King bass trombone, and a Rath bass trombone. We sound very good too.
The bottom line is, if you have quality players on each part, it doesn't matter what brand of instruments they're using. They'll be able to blend in with each other very nicely.
If you're asking about Yamahas though, they are made very consistently from one instrument to the next. Very good quality control.