
But say you might be asked to sub for a concert cycle. VERY good group, and 3 other very solid players, I think all on CC. All I have to use right now are two 100-year-old 3-valve Eb tubas. I can play pretty solidly on them, but as much as we all say we like false tones, we all know they actually stink. Especially on low Ab, which appears all the dang time.
There are going to be limitations, especially if it's new-ish music, with a lot of big low stuff. But only getting down to low B, even for whatever music, is like eating only the top third of an ice cream cone. It's good and you get the idea, but you're missing quite a bit.
And honestly, divisi/octaves is a whole "thing" that truly changes the timbre of the ensemble. Sometimes for the better especially when composers - like Sousa - know what's going on back there... but sometimes the octaves thing simply is NOT what was intended, and sounds.. well... stupid. I would not assume anything about playing it different than it appears on the page. And in the interest of not making the group sound worse, embarrassing myself, and looking like an idiot... maybe I just don't have the tools to do the job.
When I used the Medium Eb in orchestra, the pieces quite simply didn't have any stuff low enough to be a problem.
Also, I don't own the big Eb, so it could get called home at any time.
Might not even happen, so whatev'