i've listened to a lot of professional horn players as well as a couple concerts and i can't help being amazed by their tone. i want to sound like them on the higher and lower notes.

any suggestions

Proper practice is essential.
How does a pro get a great sound like that?

Equipment is part of it.
A good horn is required.
The correct mouthpiece is required.
Private study is required.
And lots of practice everyday, the correct way. Wrong practice will hold you back.
Long tones and proper center of pitch exercises.

Because professionals play everyday for hours their lips have formed to the perfect shape and are very strong and yet also able to make very minor adjustments. There is also a slight bit of callus to the lips. If they skip a day or two the callus will start to lesson and their sound will change.

Last summer I did a Hornswoggle concert of 21 horns. Some were regular symphony players and some were free lance players.
One of the audience members was a retired well known professional horn player.
During one of the talks between numbers our director acknowledged him and asked those of us who ever studied with him to show our hands. Of 21 professional horn players there 16 of us raised our hands. 16 of 21. Take into account that not all of us grew up in the same area of the United States and 16 out of 21 is a pretty good number.

So you have to study not just with a professional but someone who can teach you correctly.I know several professionals who also teach and their students suck. So don't think "a professional" is the simple answer. They have to be a good teacher. There are non-professionals who teach very good basics and then pass the student on when they reach a certain level. Ask the pros who there feeder teachers are.

And YOU DO HAVE TO PUT IN THE HOURS!