I'd like to add a couple of things. Charley Brighton plays a 2900 (different leadpipe and receiver than the typical US military band horn). He also plays a HUGE Doug Elliott mouthpiece. His sound is very different than what is typically expected from the 2900. Two FINE euphonium players play in the New England Brass Band on 2900s. Aaron Rivkin (our solo player) studied at RNCM under Steven Mead and uses a largish mouthpiece (not Schilke 51D or BB1) on a medium shank 2900. Dr. Danielle Van Tuinen (soon to be prof. of tuba/euphonium at Univ. of Florida) uses a large shank 2900 with an Alliance DC3. Their sounds could not be more different. Both are great. Danielle's is VERY dark, rich and full. Aarons is very sweet and singing.
These are three examples of really wonderful euphonium players who each have a different sound using the same (or very similar) horns. My point is that the uniformity of sound in some of the military bands where the performers all play 2900s (and generally use a variation of BB1 or 51D) is by design, but not necessarily required.
OTOH, listen to Brandon Jones in the USAF band and you hear a VERY different sound coming from his Adams E3.
Doug
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band