Best materials for tubist wanting to double on Euph

[Doc]

I promise this answer was tongue in cheek. :P (Or is it tongue out of mouth?)

I knew it was.

I wish I had something a little better, but having started on euphonium the trick to tuba ("MORE AIR") was relatively easy to figure out on a conceptual level.

I narrow it in for euph. I try to use as little pressure on the mouthpiece as possible and find the right volume/speed of air that makes it respond and sound purdy.

Maybe a better question, what specifically do you (or whoever you are asking for) struggle with on euphonium?

It's for me. I'm not necessarily struggling. What I need most is more time on the instrument. Aside from that, I do long tones, lip slurs, scales, other fundamental stuff. I do use Rochut, but I like some variety once in a while. Like Joe, I don't want to become disinterested because something becomes to habitual. A change-up once in a while keeps things going. So if euphoniumists have things they use/do that seem to work for them, or might be different, or something instrument-specific, I'm all ears. Hope that explains it a bit.

Thanks for all the responses so far!

[tokuno]

I've decided to adopt my son's hand-me-down euphonium (Sterling Virtuoso) and take advantage of his easy availability for duets before he flies the coop (high school junior). My older two are active duty service musicians, and I've suddenly & sadly internalized the sincerity of my mother's laments: "All I want for Mother's Day is to have all you kids back together for a visit under the same roof". All these years of taking for granted the joyful chaos of 4 kids, and it's dribbling away . . . .
I've been squeezing my fat lips into that tiny euphonium mouthpiece using the Brass Gym to mindfully re-coordinate my fingers (slide trigger keeps throwing me for a loop), clean up articulation, and smooth out basic slurs, which, frankly, can be any basics book, but I like the brass gym as a "problem detector". I recently graduated to Arbans, and I feel like I'll soon be able to sit-in with my son without too much embarrassment.
I can't avoid the temptation to belt out fun Rochuts and euphonium nuggets (Grainger, Holst, Mussorgsky, et al), but the "calisthentics/fundamentals" focus is helping me to avoid glossing over shortcomings (fuzz, glitches, bobbles, dynamic limits) that will surely vex me later if I let them ride.
I'm feeling like those two books are sufficient to satisfy my (admittedly modest) baseline euphonium playing requirement.