How do I smooth out violins?

Pity the pour soul who asked for advice. So far we have:
It might be the speakers and its probably not the speakers.
Buy a tubed preamp and it is not necessary to have a tubed preamp to tame digititis.
Purchase new speaker cables, ICs, power cords and power treatment.
All your recordings are bad, go vinyl.
Start by replacing the source.

I'm sure at this point he is clear on how to proceed. I guess he is fortunate, in that he gets to keep his amp (so far), and no one has invoked demon possession as the only reasonable explanation.

What would be helpful would be comments relating direct experience with the actual components in question, or diagnostic approaches that would allow him to narrow down the field without running megabuck experiments.

I think a reference recording, recommended by the group as being innocent of the offending attributes has a great deal of value. If Charles1dad has a recording of violins that exhibits good coherence, lack of grain, and lack of excessive brightness in his system, and the OP finds the recording still has issues in his system, then it is system related and not an inherent fault of digital reproduction. If, on the other hand, this recording is found by the OP to be satisfactory, then he is going to have to live with the fact that he has somehow selected a bunch of bad recordings. The idea is to help the poor fellow narrow things down without running a series of megabuck experiments.

Looking what you have, I'm not surprised that violins sound edgy or bright. Some of your components are good quality (speakers and amplifier) but "oddly combined" like the McCormick amp and NAD preamp, while others more pedestrian like the 12 year old Marantz CD changer! With all do respect, violins and pianos will only sound natural when using higher quality source components. And to sound really good, the system should be carefully assembled through trial and error, selecting based on what you hear rather than what a reviewer says.

If you are serious about improving the sound, find a good audio dealer or two willing to loan you several pieces of equipment for home demo.... at the same time. Start with the source and amplification (pre & amp) first, leaving the speakers and cables as your "control". The Spendor "house sound" is definitely NOT bright and favors classical and acoustic instruments (I've owned two models), so keep the SP 1/2E. Integrated amplifiers have vastly improved in recent years, and are a good (preferred?) alternative to modest priced separate amp/pre-amplifer combinations from different companies. (It removes some of the uncertainty.)

On a personal note, last year I revamped my entire audio system after moving to a new house. It was a fair amount of work borrowing four high quality integrated amplifiers (Rega, Sim, Naim, etc) and speaker sets (Quad, Dynaudio, Totem, etc.). But the result is amazing... clearly the best, most natural sound system I've ever owned. And yes, the violins have body, warmth, and tone that sound very real. Same with piano and trumpets, too.

Second Rrog. When getting the sound right for my main 2 channel system, I focus on strings and vocals and had in the past -for a short time- the Spendor SP1A mated with a CJ PV12AL and MF2300A combo. Not sure how much different the SP1/2E sound but upgrading the pre to a (better) tube will certainly help. Power conditioning, fuses and better power cords comes next to make the ensemble sound more musical.

Second Rrog. When getting the sound right for my main 2 channel system, I focus on strings and vocals and had in the past -for a short time- the Spendor SP1 mated with a CJ PV12AL and MF2300A combo. Not sure how much different the SP1/2E sound but upgrading the pre to a (better) tube will certainly help. Power conditioning, fuses and better power cords comes next to make the ensemble sound more musical.

Bojack - I agree with your thoughts that the NAD pre-amp may be the cuplrit (it is only a guess). I have owned and enjoyed NAD gear, but to me it can be a bit harsh at times. It is worth a try to substitute a different pre-amp if you have the opportunity.