+1 for Trackspacer.

Damn you guys....LOL!!! Another must have plug in!   Cha Ching

Well that's not nearly as much fun. :-/

jerrypettit
+1 for Trackspacer.

Do you use it?  Considering just about every mixing tutorial these days begins with the idea of notching out spectrum space for competing instruments, this would seem to be one of the most valuable tools in the engineer's arsenal.  Listening to the videos, it seems to do exactly what you would want it to do.  Are there any other VSTs out there that do this same trick?  I am surprised there isn't more discussion about this class of tool.

I think understanding the fundamental aspects of orchestral sound helps here. Within a full orchestra, especially
with 2 or more of the same instrument playing in sections, it is natural to "lose" the distinct tone of a given instrument
in exchange for a bigger, lush, "smeared" sound. That's what gives the orchestral sound its signature character.
Distinction would be derived not from EQ but from writing for solo sections for a particular instrument. Some times
this may also mean a more upfront position for a solo instrument and it playing forte while the rest of the arrangement
is written for softer playing.

I completely agree with those bringing up composition issues. Seems this track is done though. Perhaps though the piece could be rearranged so the interfering instruments are swapped out for less intrusive ones in terms of cello/violin tones.
 
Also agree with adjusting the "feel/timing" of those instrument's performance. Let the background orchestra be more rigid providing the tempo of the piece and the solo instruments be more fluid. This might be hard to do with the PRV though but certainly not impossible with good ears and intuition.

Oh and I don't have one readily available but there are plenty of diagrams of orchestra pits and how they are seated. This can be a useful guide to panning your instruments which will help them cut better. There is a reason orchestras are seated the way they are. This can translate to a mix as well from what I've read. Worth a look. Very interesting stuff.
 
Then I guess your solo instruments would be centered and turned up and perhaps widened a bit. I'm not experienced in this type of production though. You may want to post down in the Techniques tab for more info. There seem to be quite a few classical guys lurking about.

Hi cparmerlee
 
I use the trackspacer. It's a very handy little plugin and it's just a matter of using a send to the track you want to duck. I usually start with its default setting then adjust from there. It has the capability to isolate the frequency range you want to affect with a high pass/low pass filter built in. It doesn't give any information about the frequencies it's working on though, but I'm sure that could happen in an update.
 
But having tried it on various things, it really does work well.  It adjusts to frequencies in real time or you can freeze it. Maybe surprisingly, it works well on sparse mixes say, vocal and acoustic guitar. (You'd simply insert a send from the vocal to the guitar buss and Sonar will give the option of sending to the track which contains trackspacer )
 
Not so good maybe at creating space for a vocal against a whole full on backing track as you may hear the ducking. So you have to be a bit more selective about the instruments sitting in the same frequency range within the mix that you want to duck ... if that made sense!
Definitely worth demoing.
 
As a plugin, it could work for the OP's predicament ... (in combination with all the suggestions above about arrangement etc.) If the cello is playing arpeggios (original post) it's maybe covering quite a large note range quickly. The trackspacer would adapt to that as it goes along.

One note on the orchestra seating chart:  I keep that handy when trying to create a realistic orchestral mix, but I don't personally think the chart always applies to pop music:
 
• The whole orchestra is seldom present in a pop track.
• The seating chart was planned a long time ago with the goal of presenting an even, balanced sound to the audience in an auditorium and grouping players in a way that is logical for them.  Pop records have different goals and usually have more different imaging.  For example, in a pop record, you wouldn't want basses off-center and you might want to spread the string section out differently.
 
Still, the chart is an excellent reference.

Good input, Konradh. I really haven't dabble in that kind of thing yet but had read about it so thought it might help OP. I will however keep what you said in mind for any future attempts I make. I know you work with synth strings quite a bit more than most of us from your posts.
 
Any thoughts on how to deal with orchestral rows? Like creating the effect of how far a specific row is away from the listener? I'm assuming delay might be the answer. Cheers.