Symphony #1

I’d like to say I write symphonies;
choral epics for unpitched voices,

Making up words is cool by me when done well. The premise of this is a little bit too grand for me, but then comes:

heart-snagging uppercuts
that lift like Scorpion fatalities

OK, I recognized this from the movie Mortal Kombat, and I broke out into laughter! "Heart-snagging" suddenly takes on a whole new meaning, and the reference breaths irony into the narrator. One issue I have is in the metaphor "uppercut" only because it lacks the double meaning of "heart-snagging" and thus makes redundant the simile in the next line. So it overall feels like a bit much here.

and hang readers breathless in
Tolkien-sized meat lockers.

This just went a little off the imagery deep end for me, without really enriching the lines around it.

I’d like to say I cut wars into
line-stone effigies, that are
not Alexandrine in iambs

Do you mean to say "lime-stone"? Because I'm lost as to what you are evoking with "line-stone." The only thing I can think of is a play on words in which lines of poetry are being referenced. Feels like a stretch to me. Now, "Alexandrine" as an adjective does not demand capitalization, but I'm taking the capitalization as a hint towards Alexander the Great, as indicated by 356BC and the general history themes that are present. Not to mention you correct us in thinking that it's about iambs. I liked this. It was playful and really evoked the meaning that you're getting at.

but in three-five-six-BCs and
seventeen-seventy-six-ADs and
haughty, histrionic,
historic tethers.

Spare us the tiresome alliteration. It just comes off as self-indulgent rambling here, and we're already being patient at this point. :p

This stanza overall was alright. The first line is a good device to hang the rest of this stanza on, but I feel as though the ending needs something to hold it all together, since the whole stanza is merely expounding on the first lines.

I’d like to say I write works of
panorama and spectacle---symphonies,

OK, bringing us back into the rhythm and context here. I recommend using something cleaner like this em dash character: —

ballads, metric opera magna---
but never anything as straight and
simple as a poem. Indeed;

Why did you put magna after opera? It only managed to confuse me.

call it verbal rapture, dictated
cataclysm, monolith and
temple of rhyme, but I have
never written and will
never write a poem.

Nice ironic and rhythmic conclusion. Perhaps ease up on the grandiose amount of descriptions for one thing, it feels uncontrolled. Then again it does serve the humor in the poem's concept. Overall this piece* could use a bit of trimming and depth but good job.

*edit

Haha. I had to laugh at the end;

I have
never written and will
never write a poem.

Seems enough to point of the obvious that you indeed just wrote a poem. My favorite part was;

I’d like to say I write works of
panorama and spectacle---symphonies,
ballads, metric opera magna---
but never anything as straight and
simple as a poem.

Anyway, personally I think it's ajob well done and that you shouldn't change a thing because changing it would be devasting. I hope to you that it stays the same because I thinketh it just perfect as it be. Great job and please, forever may you write(: