Attacked by the Music Monster

(Warning: if you weren't a music major in college, you might not have any idea what the hell I'm saying here. Feel free to keep reading anyway, though, if utter confusion sounds like a fun way to spend a few moments).

It's almost 4:00 in the morning and I've spent the whole night working on my band piece.
The pupils of my eyes have dilated into eighth-notes. I think the left one has a sharp next to it.)
And I'm still not satisfied with the instrumentation.
We rehearsed this a couple times, about two years ago, and I was NOT pleased with it. So displeased, in fact, that I put it away in my "maybe someday" folder... indefinitely. But I've taken it out and re-worked it, in hopes of giving it another try at our rehearsal on Tuesday. I've added some parts that weren't there before, and taken away some solos that were there before. I've added harmony where previously there was unison, and I've changed some harmonies that seemed to clash too much. I've switched parts and octaves and intervals and... well, let's just say I've spent a lot of time on this. And I really want it to work out this time.
Part of why it sounded so bad last time was that we didn't have a proper blend of instruments, and some were absent altogether. (for example, there's a nice important deep rumbly part I gave to bassoon, bass clarinet, and bari sax... but none of those people showed up except for bassoon. Bassoon all by itself is NOT loud or rumbly enough.) Plus, the dynamics were not played correctly, there were wrong notes and intonation problems and rhythm problems and tempo problems... I think we rehearsed it twice, and both times just about made me wince in agony.
The thing is, it sounded GREAT when I played it on the computer at home, with my composition software. The score was 'correct', as far as the notes went; I just wasn't happy with how it sounded in person. Maybe if we'd kept on rehearsing it, we could have nailed down the problems and 'fixed' stuff... but we didn't. And so it has sat in my folder for the past two years. Since then, we have performed other stuff I've written, so maybe the time has come for this particular piece as well.
So I'm hoping to have it all finished on Tuesday, with all the instrument parts printed out and ready to distribute at the rehearsal.
Hopefully we'll have a good group there, with all the instruments I need, and good musicians to play them.
That's not too much to ask....
Is it?...?