Tips for Mixing Orchestral Tracks?

A good starting point would be Dimension Pro. There are several expansion paks and other goodies in it to try out. 

Work your midi CC's like crazy. Listen to real orchestras and try to get as close as you can. I send all sections to a dedicated bus and use the bus compressor on each section to even them out a bit. With EWSO you shouldn't need reverb as the samples have a ton of natural hall sound on them. While they are already panned in their orchestra seating I will pan a bit farther out to taste and use Channel Tools sometimes for a wider sound. I normally have vocals and electric bass going in the center so it helps with the mix to get a bit wider sound. 

One of my favorite plugins for mixing strings is the Waves TG12345 channel. It has a very sweet EQ that adds presence to strings without adding harshness. Really, other than EQ and a good reverb, you should not need to add much else to a pure orchestral arrangement. You want the wide dynamics to remain, so compression should be used very judiciously, if at all. Now, if you are mixing orchestral stuff into a pop or rock song, then you'll need more compression to get everything to sit well and be audible.
 
Regards,
Dan

RobWS
What about the use of console or tape simulators?  How about the SSL bus compressor?

As we always like to say about mixing: if it sounds good it is good.  Adding some warmth courtesy of vintage fairy dust provided by emulations of classic gear could indeed make things nicer.  There are innumerable options here.  Some of my favorites come from Nomad Factory (the Analog Signature Series and the Pulstec EQ in particular).  With Nomad Factory you must be careful not to overdrive or the sound degenerates to crap.
 
As to using a bus compressor, the only caution is to not remove the dynamics of the original sound.  A real orchestra has a huge dynamic range and composers often take full advantage of that.  It would be wrong to remove that from the original recording (even if the recording was done using virtual instruments) with compression.  On the other hand, compression with an extremely light touch using a vintage-modeled plug-in could be delightful.  Same with tape simulators.  Just experiment and see what floats your own boat.

This forum is more focused on orchestral mock ups and arrangements. You may find really helpful
https://vi-control.net/community/

Well it depends on the sounds and quality of the sounds. If the violin has a high mid problem, I tend to use a linear phase EQ, because I know I'm going to use a lot more EQ down the line, same with viola. Over the EQ I will tend to place a tape sim for volume leveling...I use the J37 from Waves, but you could use Sonar's pro channel variety or even Wave's master tape. I then place Waves NLS summing plug and send that into a buss with a compressor...something tasty depending on the NLS setting. So if it was a Beatle type track a Fairchild. Oh and I forgot, I tend to use a double fx, either Wave's Doubler or Wave's ADT.

For brass I tend to use a tasty EQ, Wave's V series EQ is good. I also like the Redd EQ for a simple EQ, I then tend to send the individual brass tracks into an Aux or buss where I will EQ again, I will probably use a tasty compressor the VComo or SSL by Waves and probably a J37 again...not in that order though. Oh and an NLS summing plug.

These are just basic settings, I tend to mix it up a bit depending on the sounds and track. I also like to double the string instruments with granular versions of themsleves. And Wave's CL2A is great for anything to do with strings...even mastering. Oh and sometimes I will use Wave's Brauer plug to move things about in a 360 degree field.

It might sound like a lot, but...it works and It's how the rock avant-garde or their production team did things...layering.

Sorry, I use Notion 6 for my orchestral instrument - and in fact all my midi sequencing these days...but I tend to do some edits of midi in Sonar.