LOL - interesting revival of an old thread @lbrookins - and - I should add, a Big Welcome to the forum - enjoy your time here !

Referring to your "do you think a violin, even played softly, would be too shrill of an instrument to provide background music" question - that's interesting.

I've been playing just over 5 years and personally, I find the "top-end" (and I'm not referring to high shifted positions, just the E string up to the C6 - which is ONLY just over 1Khz !!!) "irritates me".  I find it intrusive.  

See what you've done?   I have to argue / discuss this now with myself.....  Here we go - hang on !

(1) Perhaps it is because of my age and the normal frequency-response drop-off that occurs as we get older.  Human typical hearing range - 18Hz to 20KHz - nah not any more, my frequency cut-off is around 13kHz, but even so, I find the E5 upwards just plain irritating.  A bowed string creates an approximation to a triangular waveform, and a good instrument will contain harmonics, possibly up to the 15th or even 20th - BUT - even the 20th harmonic of 660Hz is still only 13Khz or so (and even so, it will be a VERY small contributor to the final tone).  SO, that's not likely to be the reason I find these frequencies irritating.   Oh well, good try, but no cigar.  Next thought....

(2) When I play, I am largely soloing, although on occasion, yes, I get the opportunity to play either with a backing track, or with others.  Now, THAT is *instantly* different to my ear.  Several things are going on in this situation.  These are - 

(2a) The other player / players are playing different parts - there are playing in harmony - chords, or at least partial-chords even with 2 players, are occurring.  I find this a much more satisfying sound-scape.

(2b) The other player / players are playing exactly the same line as I am.  Well, that is RARELY if ever true - the intent may be so, but, no, they/we as players are NOT playing with *precisely* the same intonation, neither are we playing with *precisely* the same timing, and finally, even IF (not possible, but IF) we were all perfectly intoned and perfectly timed to each other, there would, at an individual waveform level, inevitably be a *phase* difference between us.  Interesting.... So, again, I find this a much more pleasant and comfortable listening experience.

Well, that was interesting (to me anyway!)  And equally, although I play fiddle tunes and folk music, I listen to a lot of classical music,and violin concertos, well, they are awesome - I love the more complex sound of the multiple instruments. 

As it happens, for soloing, I already have the answer - and that is to use a viola-tuned fiddle, low C, then the normal G, D, A and I'll play the tunes either dropped by a 5th, or even a full octave down.  That works for me, sounds real pleasing to my ear- and - well - depends on the piece - but - I would rarely even play on the top string ( the A ).  That's fine of course, but it's a bit of an issue to play with others playing in the tune's normal key LOLOLOLOL

Sadly, in reference to the auditory frequency range of humans, yes, I just thought I'd go investigate a bit further- and I found this rather astonishing research - 

Attribution : By Cmglee - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/.....d=35890958

And, if you don't want the wiki detail, here's the graph - 

I just found it awesome that someone researched this !!!!  Cool !