How do I smooth out violins?

IMO, you should decide on one of two approaches to solving the problem: 1. tackle the problem in a way that will give you long-term satisfaction according to your tastes and priorities by intelligent system building, or 2. use band aids now to tame a specific problem that will "help" this specific problem, but inevitably take the positive possibilities of your system.
Huh, you say?

1. Realize that the problem you are describing is a common (but not necessarily a deal breaker) problem with digital recording AND playback. This gets better all the time with new technologies and refinements of old, but compared to the sound of live strings, you will probably have to accept less-than-perfect at a price level anywhere near what you are talking about. There are many really good digital orchestral recordings as Almarg recently reminded me. But, there are an awful lot that exhibit the problem you are describing, and it won't matter what equipment you use for playback. However, the CD player can aggravate the problem already on the recording. So, that's where I would start. I really like the Ah! Tjoeb (Marantz
based) CD players in the budget level. It uses a tube output stage and sound fantastic with orchestral music. Always remember: any problem that is created by the source component will be there all the way to the end of the chain. You can mask it, but you will also mask information that you do want.

2. You can mask the problem. Some good suggestions above with cables and tweaks. Personally, I don't recommend taking that route. Your speakers and amp are solid, the CD player and pre, less so IMO. Tackle the problem in a way that will make you happy long term.

My two cents. Good luck.

Maybe I am showing my age. But, that the idea that massed strings are problematic on many digital recording/playback (I agree with Jmcgrogan) should come as a surprise at all is, to me, the biggest surprise of all. This has been the subject of discussion for as long as digital has been around. Clearly, there are many fine digital recordings, and in some ways analog has as many problems (if of a different kind). But, the OP seems to be familiar with the sound of live strings and is looking for such. Given how common the problem is, it seems to me that the source is a great place to start. I really don't mean to turn this into a digital vs analog issue, but I have heard VERY few digital playback systems playing back mased strings, that allow me to forget that it's digital that I am listening to. Then again, I have heard just as few turntables that let me forget that am listening to a turntable. Is that pc (I don't mean power cord) enough?

Gear has a long way to go still; if the sound of live is the goal. The notion that a $400 CD player is "without fault" seems a little far fetched to me.

IMO

Bojack, you want this! ;-)

http://app.audiogon.com/listings/cd-sacd-players-ah-njoe-tjoeb-4000-cd-player-2013-01-09-digital-02790

(No affiliation with seller)