Well a few tips would be…
Consider using reverb not just as an effect, but to emulate a microphone in the recording space somewhere.
So if you think about how big you would like your room/hall to be and where you’d like to place it, then solo it and imagine you were listening to a mic recording from that part in the hall. Visualising this should help you to find tune it. You also might want the tiniest bit of saturation as all mics have their own character and non-linear responses. If you want to emulate vintage sounds then the AR King’s Mics might be good for that, otherwise you could try Saphira, or their MDMX Overdrive. Just the tiniest amount though. IR-1 has a few good halls too, but EW Spaces have quite a few of them!!
Use pre-delay to stop the reverb muddying up the transients of the instruments
This is also handy to help emulate that “mic in a room” thing as sound will take longer to reach a car mic as it would a close mic. About 3 meters per second, give or take. Keeping reverb away from the transients helps them to punch a bit more. Or you could simply stick something like H-delay in front of the reverb, turn feedback to minimum, mix to full and you can use that as a predelay as well. The advantage of that is its Analog modes have different types of saturation, so you could use it to do the two jobs.
Try to use samples from the same library as it creates for a more consistent sound.
But if you are working with several libraries, use less of their “room mics” as that is where the bigger differences will be, and use more of that reverb I mentioned above. If it sounds close enough to a mic in a room and all the instruments are using it, that’s how you’ll get s more cohesive sound. It helps if you are using mostly close mics and try to balance the mics in each sound so the do sound like they could be coming from the same place.
Consider using the tiniest bit of chorus on your reverb or instrument sections.
Not enough to be heard, but more “felt”. Same with the saturation I mentioned earlier. This is because even though we tend to work with quite deeply sampled instruments they can still tend to sound a little static. These instruments were recorded in isolation so there’s no bleed that you would get in between the mics as well. So the chorusing is a way of introducing subtle pitch changed between each player and the slight phasing effect you get when instruments bleed into other mics. So the idea is to make it sound a bit more organic and a bit more like it was all recorded together in the same session. After all, that’s what happens with real orchestras. I been using NI’S Choral for this event lately, I’m not sure what Waves has that does the same thing, though.
I have other tips as well, but not enough time to write them all down.