Mael,
Once again, you're stretching my ear in a good way! I think my comments are of the "picayune" variety...
They mostly concern very small harmonic changes.
-5:13--the I-iii-II7-V progression seemed a little "unconvincing" (when I use that word, I always mean it didn't "pull my ear along;" it didn't seem like, "ah, yes; that's where it should go." Of course, you can set up one expectation and then surprise the listener, but this didn't seem like an "oh, wow!" surprise either). In some sense, it's just my opinion, but also iii-II isn't a very strong harmonic motion. The fact that the motion is just tutti chords here makes the strength of the harmonic direction even more important; I'd try for even stronger.
-4:46--The 7th chord and descending chromatic line that signal the wrapping up of this small section (was this some of the C theme?) came a little too quickly for my taste. I'd loved to have heard a little longer initial statement of this theme, even if you intend to develop it later. This really is totally preference, so take it or leave it.
-5:29--The Bb7 here is a nice surprise, but the phrase afterward continues as if it didn't exist. It seems to me like a brief trip to a feeling of Eb as tonic would complete the idea and make it sound less like an excited outburst, which seems incongruous with the majestic mood here. If you're going for humorous or even just slightly whimsical, then I think it works.
5:57--In this 3rd statement of the phrase (which began at 5:50), a very classical thing would be a deceptive cadence to F (VI). The F would replace the d chord (I believe this is the 4th measure of the phrase). Right now your harmony is iv-i-V-iv and then another phrase iv-i-V. I'm saying to do: iv-i-V-VI and then iv-i-V, perhaps with something else in the middle (possibly vi?). The 2 iv's next to each other and the movement from V-iv is slightly weaker to my ear. One OTHER possibility here would be to cut the 1st phrase short, having iv-i-V and then starting the next phrase as an interruption, without the 4th chord in the first phrase. This might be a nice surprise!
-6:11ff--Here, the winds have several countermelodic theme "snippets" that seem jarring against the main harmony. For the first wind entry following the first string phrase (6:11-12), an underlying harmony of N-V-i would fit closer with the wind fragment, provided you raise the 4th note of the fragment (a 7th). However, this Beethovenish cadence formula is probably too final sounding for the 1st statement of the sequence, so I'd tailor your wind fragments to match the main harmony you have, which works nicely. If you're going intentionally for the dissonance, that's fine; the "rub" seems a little out of character with what you've done elswhere so far, however.
-6:24-5--Wow

. You stretched my ears here! The interesting change from EM to C can definitely work, I think. Try to listen objectively to see how you might make even this novel movement more strong. One suggestion I'd make is to keep the lower voices on E, even while the middle voices alter the harmony, until the melody reaches the C on the next downbeat. This will keep some continuity from where you "came from" to where you're "going."
-6:29--I can tell you were earnest and passionate here, as you said. Even after listening several times, the high register spot in the violins still sounds "not-quite-right." Even though there's a suspension, I don't think that's the issue. Here's a couple possibilities to keep the passion and minimize any possible oddity in the sound:
1) keep an extra measure of vi (like you have on the measure with the high register vln. suspension) to keep some continuity after the startling violin sound (ie, spread out the changes: first violin dissonance, then a measure of "buffer" before another harmonic change). The extra minor may also help keep the passion up. You could then move to IV and ii or V.
2) if you really prefer just 1 measure of vi (where the vlns. have the high suspension), then make sure the inner voices don't anticipate the change to F early. Because I heard what sounded like suggestions of F in the inner winds on that very same measure (w/ vln suspension), my ears were overwhelmed by too many changes, as I said before.
I had lots of things I liked, especially some of the continuity with variety in your development of previous melodic ideas, but I figured I'd just stick to the picky suggestions. Hope I'm not being to prescriptive. Only take what you like/what is helpful.
Brooks