Well, big band is a little different from orchestra, but some of the same things apply. You need to be careful with your layers. Brass octave sounds are a particular culprit, and you can't use them over much of a range before either the low note goes down too low, or the high note goes too high. REAL horn sections, even in tutti, have players drop down octaves as they approach their range limits (or up).
If you are triggering the arranger while doing all this (you didn't say you have a rhythm section), things get a LOT harder. The whole thing about orchestral and bigband voicing is the SPREAD of the chords and playing. Most chords are 'open' chords, in other words, wider than you can play with one hand. They are fairly easy to pull off if you have two hands, but if one is running the arranger, things get tougher (but not impossible).
This is where your Pianostyle mode can be REALLY useful. Now you can move about the full keyboard, play sounds through their natural range, and still play unison or octave lines that don't retrigger the chord recognition. I am afraid I don't find the Melody Intell all that useful, but it has it's moments.
Most of what I play for bigband as far as tones goes revolves around a three way layer. Usually, I'll get a brass section sound in unison, layer it with a sax sound with good timbral change (listen for different sample layers as you play louder) and some nice sampled vibrato. Usually one of the breathier patches (I use alto sax vib on my G70), and I'll set them to Medium keytouch. Then I add a brass section swell, layered up so that, at it's loudest, it just pushes the sound a bit further (in other words, don't let it swamp the saxes until you are hitting as hard as you can), and I put that on HIGH velocity response, so it pops through a lot more as you play louder, and disappears in the quieter sections. This is one of the main tricks about getting realism from brasswinds... have different velocity responses for different patches, so the timbre as well as the volume changes as you play harder. Keep your saxes as the main 'bed', then let the brass punch through on harder hit notes.
You COULD actually restrict the velocity ranges so the brass swell doesn't play at all at lower velocities, but I find that makes for too jumpy a note response. Keeping it on HIGH will pretty much make it disappear at lower velocities.
OK... next the voicings themselves. Have you ever played in the 'George Shearing' piano style? This is where, to keep it simple, you basically play the melody line at the top of a two handed chord, AND the bottom, and then you fill in the chord on the inside. It's a sort of 'block chord' approach, with the line doubled high and low. It can be played 'close' with only an octave between the line, or opened out to two octaves, which gives you more freedom to pick how you voice the chord. It's pretty good for getting a bigband section sound, and has the advantage of, in pianostyle mode, still triggering the chord recognition pretty well.
Practice this if you haven't got it mastered yet, to the point where you can block around fairly simple melodies with all the implied harmonies added as you go. Now, in Pianostyle mode, you can block around for a while, and if you get to a point where the chord doesn't change for a bit, play the melody ONLY, either just the one note, or in octaves (you have to be VERY clean with your fingering in octaves, lest you play THREE notes accidentally, and your chord recognition goes haywire!). Instant bigband!
This ought to get you going...
Some more advanced things might be to have all five parts layered over the whole keyboard (UPR 1,2,3 and LWR 1 & 2), and have LWR 1 & 2 be more of a clarinet and sax layer, then program your volume pedal to be all the UPR sounds when down, and LWR sounds when up, and now you can get even more variety...
I hope this helps with what you are trying to do. It takes a while to get your head away from pianistic chord voicings, but hopefully, this will suggest a start.
I am also a big believer in the 'sponge' theory... If you restrict your music listening to JUST bigband recordings for a month or two (and keep it simple stuff... no point listening to Buddy Rich or Woody Hermann!), an awful lot will just seep in and get absorbed unconsciously. The main trick is KNOWING deep in your heart when you have played something that sounds right, and more especially, KNOWING, at a gut level, when it sounds wrong! Then, keep doing what sounds good, and stop playing what sounds wrong (
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) and pretty soon, ALL you are playing is what sounds good..!
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Best of luck...