How do I smooth out violins?

I agree with the advice of those who suggest addressing the recording it self.If you find it is`nt the recording then I would next approach the AC power quality(this can make a significant difference) and audition some very good conditioners.If that does`nt solve the problem only then would I proceed to improving the quality of the CD player(source) and the preamp.As has been said already, you need a good recording reference as the first step.
regards,

If you are not satisfied with the sound you most likely need to change a component. A tube preamp is a good place to start. The question is what tube preamp will mate well with your system? The Quicksilver full function preamp has extremely low output impedance and will match with any amplifier. This also makes it less sensitive to cables. Trying to find recordings that sound good with your system doesn't make sense. It will shrink your CD collection to a hand full of recordings that you will listen to over and over. A power conditioner at this point would be nothing more than a band-aid.

Always follow the signal when auditioning a substitute component. So,that said,start with your source and continue downstream. My gut feeling is your CD player and your preamp are the culprit. Don't rule out better power cords(VH Audio power cords are very good for the money)and power conditioning as mentioned earlier. Power is everything! ICs and speaker cables would be the last resort. Get your components right first. BTW, No affiliation with VH Audio.There are a ton of good power cords to try.

A number of good responses above, including your own regarding changing tubes. I have experienced some dramatic benefits from this in my system. As someone else hints at above, finding ways to lay back the sound is most desirable. I used to favor a more forward presentation, but the desire for a more relaxing, listenable sound changed that. A caveat, though, mirroring what someone else indicates above,is that some recordings of violin are too closely miked and/or poorly made, and as such might be immune to virtually any kinds of alterations in one's system. An example(at least in my experience)is David Oistrakh's performance of the Beethoven Violin Concerto with Andre Cluytens on Angel. Also, in general, I have always found the blue label Angel classical recordings to be somewhat bright. Aside from Cardas, you also might want to consider one of the lower priced Purist Audio cables,e.g.Musaeus.

I think there are a lot of good comments above. I am especially appreciative and supportive of where frogman was going, in that you really want to diagnose and address the problem rather than throw bandaids at it. Who among us appreciates the auto mechanic who fixes our cars by sequentially replacing parts until the problem goes away?

When I read the OPs comments, I focused more on lack of integration than lack of smoothness. I think most of you focused on smoothness rather than integration. This is where the comment above that this may be due to more than one issue is also relevant. Further clarification from the OP is required with respect to what he means by "smoothness." Does this mean you are experiencing excessive grain or excessive brightness? If it is excessive grain, I strongly urge you to replace the aq4s. They are very grainy, but I did not find them overly bright. If the problem is brightness, then some of the comments regarding power treatment and IC's may well be relevant to this problem. If dirty power is exacerbating the problem, it will probably be variable. Most people have cleaner power in the evening than during the day. If the problem is not variable, you may not want to address power treatment first.

My guess remains that the "integration" (coherence) problem is speaker related. I have no knowledge of this speaker. If those who do can indicate that coherence is a strong point with this speaker, well, I guess the problem must lie elsewhere. I can tell you this. I had major issues with integration (lack of coherence) and also a minor issue with stridency or harshness in reproduction of violins (at the crossover frequency) that pretty much completely went away when I went from Magnepan 1.6QRs to 3.7Rs. I have an extensive library of orchestral and chamber music, and I would have to go back to cds recorded in the early 80's to find examples of recordings where the violins are excessively bright. Granted, certain recordings can make a violin sound larger than life due to close miking, which I suppose could be a part of the problem here. But I find it difficult to believe that the OP has somehow managed to selectively collect a large number of bad recordings.
I do have a tubed CD player, but I do not have a tubed pre amp. I have nothing against tubed preamps, but they are not a panacea, nor is vinyl. Digital can get this right, and will not require investing in a top notch vinyl rig and phono preamp. Resorting to vinyl is not really a viable option for those who have a substantial investment in CD's, and I would suggest most fans of classical would not be satisfied with the quantity of music that is available on vinyl as compared to digital.
One other possible issue here is jitter. I don't know the Marantz, but in my experience jitter will for some reason manifest itself as most objectionable with music that is rich in high frequencies.