I'd suggest you think of this as a "focus" issue.
If you want your listener to be able to hear the oboe solo, you need to
guide them to focusing on that element.
Think of an orchestral sketch - the basic musical functions are broken out as:
- Melody
- Counter melody
- Harmony
- Rhythm
Sure, the roles can be assigned to different groupings of instruments over time, but as a rule of thumb, there's only
one melody at a time.
Consider of how a counter-melody is distinct from a melody: when one is active, the other is generally less active. Make it easy for your listener to hear the important bits.
Similarly, while harmony has a rhythmic and melodic element, it's done in a way that signals to the listener that it's not the main point of focus. A non-orchestral example would be a rhythm guitar - it can play a cool and varied strum pattern, but it better not overshadow the melody.
If you want an instrument to have a melody, the other instruments need to be relegated to roles that are subservient to the melody, so the listener can shift their focus.
If you want attention on the oboe, why would the orchestra be going full scale? You're signalling to the listener that they should be listening to the big, loud orchestra. What clue have you given them that they're supposed to be paying attention to the oboe?
Imagine bringing the whole orchestra to a sudden halt and then bringing in the oboe.
That would be effective!
Keeping other instruments out of the melody instrument's range is just good arranging. Sure, if you've got a piano competing with a vocalist in the same register, you can try to EQ space in the mix. Or you can tell the piano player stay out of the vocalist's register and try
accompanying them instead of soloing.
So yes - orchestrate things is a way that make it easy for the listener to focus on what you want them to hear. Focus can move from one instrument to the next, but at any one point in time, your listener should be able to confidently know what they're supposed to be paying attention to.
And if you really can't remove the competing frequencies from the mix, you can use something like
TrackSpacer that'll do the work for you.