How do I smooth out violins?

Power conditioning is a practical first step to consider because if done right, ie a reputable product with ample power/current delivery for the task at hand, like Furman line for example, the result is usually always positive regardless of systems sonic "flavor". It is fundamental in that sense and sets a good foundation for the rest. Other changes will affect the sound in various ways that might be deemed positive or negative, depending on user's tastes. Cleaner power pretty much is always a good thing! I would use a conditioner with the pre-amp and all digital source components (players, DACS, etc.), but not on power amp to start. Power amps consume more power and current and require beefier and more expensive power conditioning for effects to be assured as positive.

Power conditioning on the front end will indeed make a big improvement in this area. I have tried many and always come back to a BPT balanced power unit. I am continually amazed on how much the BPT improves the music in my room.

Great on a digital front end. Removes glare, noise, sizzle in the upper frequencies, separates out the instruments in their space ....etc

I use a BPT 3.5 Signature. I cannot overstate the impact. Mixed bag on amps, but a must on a digital front end and preamp.

Get better equipment or roll off the highs.

Put some DNM reson speaker cable in place of AQ4, will probaly do it for under 200 bucks.

Some very good suggestions and I agree that you should have a reference CD. That said, when I mentioned earlier that I changed my cables, it was the final step to my system.
I agree with those who say start at the source which is your CDP and next the preamp. I also agree that all systems need power conditioning or filtering (I use a Furman), but I think you can find the cause of the harsh highs before heading down that path.