Intriguing source material to say the least. It's always fun to see how different composers are inspired! I'm sure you have made 5 tuba players somewhere very happy. It doesn't seem like they get much solo material, and here they have 4 minutes of uninterrupted bliss.
(NOTE: If you could be ever so kind as to post a PDF of the score so reviewers don't have to follow along on YT (such a pain to navigate back to when writing reviews), that would be much appreciated!!)
Now, let's talk about the music.
The aleatoric sections that bookend the piece are a risky choice and not one that adds much value to the listener's/reviewer's experience in my opinion. I feel that such a choice requires justification, as the rest of the piece flows in a more traditional manner. If it's just to "shake things up," that's well and good; there are other ways of doing that without a clashing of musical styles.
We also should consider the enjoyment of tubas 4 and 5, who are relegated to playing repetitive quarter notes with rare departures to other note species. I find myself asking if removing them from the piece would significantly alter the message, and I feel the answer is "no." The bass drum provides us with a driving rhythm (and will probably drown out their parts, anyway), and even when these lower tuba parts don't echo the drum's rhythm, they copy a higher tuba's part in octave. I suppose my point is that you could likely achieve the same—or nearly the same—effect by completely removing those 2 parts.
I did enjoy the minor rendition of Kyrie Elaison, especially the contrary harmonic motion between the 1st tuba and the others. Counterpoint was sparse but it was there, so kudos for that! The articulations, however, were overdone. I think the piece would've sounded roughly the same if even 75% of the written articulations were omitted. Also problematic is the passage beginning at M79, where you have the tubas play, in unison, a D1 at a dynamic of ffff. And have them hold it for a whole note. With an accented articulation. In tubas 4 and 5, this is followed shortly after by a series of low, loud, and long dotted half notes. I'm not doubting the physical possibility of this, just that of your players. And why risk it? If you want loudness (or the illlusion of loudness, which is often just as effective), try breaking that unisoned D up into a chord (a nondiatonic one for extra points). The sound is spread out over a wider range of frequencies and the assault on the eardrums more pronounced.
All in all, I think this piece has great promise. I enjoy the choice of instrumentation and find the source material unique. If you wanted to sink some extra time into this work to clean up the articulations and "fatten" out the partwriting, this piece would really shine!
Best,
Jörfi