Hey Henry this is a really awesome piece! I want to spend time going through the whole thing, but for now I focused on the Third Movement, but I will move on to the others as I find time.
I'll start out by saying your counterpoint skills are extraordinary! You have a gift for constructing fugues, and you're very good at taking small motives from your themes, developing them, and passing them between voices. You're also very good at using chromaticism and shifting between different keys to keep the listener interested.
I also really liked the overall structural concept. It appears you have three main contrapuntal sections (two minor, one major, then recap the minor at the end) that are separated by tutti moments that provide structural cadences. I think this helps the listener breathe between the complicated contrapuntal textures.
I will say I think you could have done more of this however. What stuck out to me is that you don't revisit the opening motive until the very end of the piece (unless I'm missing it somewhere...). I think a way to give the the piece even more structural unity would be:
Extend these tutti "breaks" between your contrapuntal sections. At the moment they seem a little short.
Use them as opportunities to develop your the opening motive more. I think if you were to take the opening motive and expand it when you come to these sections it would give the piece more unity, and make the development along the way more clear. Right now I only hear the motive at the beginning, and then 15 minutes later at the end, so it's hard for my tiny brain to see the connection lol.
A good example of this would be M50. Maybe have the clarinet play the opening motive here instead of the sixteenth note figure? I also think this could be expanded a little more to give the listener more of a break before launching into the next fugue. Right now it just seems like this is forced in so you can begin the next contrapuntal section.
I did take a fairly deep dive at a couple of parts on the voice leading and found a few spots that stuck out to me:
At 32:40 - the resolution from beat 3 of M33 to the downbeat of M34 sounds a little odd to me. I think it may be because you have a parallel fourth motion between the Eb in the viola and the sounding Ab in the Clarinet going to a D in the voila and the sounding G in the Clarinet. Perhaps a solution to this would be to have the viola sustain the D instead of raising up to the Eb?
33:31 I also found the resolution at M45 to be a little odd. The Eb minor here sounds out of place to me, since we're in the key of Eb major, and since the ii-V in M44 seems to set up for a I in M45.
At 35:25 - the descending sixteenth notes stick out to me, I believe because there are parallel tritones between the Clarinet and Vln II.
I think my favorite part of the movement is the return of the minor motive at M170. To me this brought the piece full circle and provided the "a-ha" moment of the piece for me.
Overall I think this is excellent! Your counterpoint skills are a definitely a strength. Throughout the piece you are able to weave five independent voices between each other and keep each voice melodic and interesting. What I would suggest you work on are the simpler textures. I think if you were to extend some of the "interludes" between the contrapuntal sections this piece would be next level.
Thanks for posting! I thoroughly enjoyed listening to this. I will definitely look through the other movements and give feedback when I can.