Adding Wagner tuben is pretty much the last comment I would have expected! Sadly, my orchestra doesn't own them, though some folks in town have Jinbao tuben (which aren't great). So, I don't think that's going to happen on this chart... but what I can do is play different instruments (I have four, and access to more), and different mouthpieces, and vary mic placement a bit.
All of this feedback is really useful and appreciated! I think a lot of these issues can be solved or improved pretty easily... The score is a little sparse on dynamics and articulation markings, and that's an easy fix for varying tone colors and pacing, and reducing repetitiveness.
There's only one short section that has no original source in it, and that's for about 3 bars at ~5:43-5:48... and now that you mention it, it does feel like something's missing there.
The only other ostinato that gets played without any melodic material over (or under) it is this stuff...
... which is actually straight out of the original source. It's also in the horn parts of the orchestral arrangements that I've played, which is why I let it be so prominent... It's one of those things you hear a lot during the first playable section of the game.