Hi Dominique
Here is another approach - the approach via your ears and the speakers/phones.
Use one of the Suite EQs. Chose a "bell-filter" with a low Q (0.3 -1), boost the EQ (+6...+12dBs) and scan through upper frequency-range of the strings sound. This way you will find the most unpleasant frequency range for a certain situation. Now turn down the EQ to the minus gain (-3dB, -6dB,..) until you like it.
Try a highshelf filter as well. Use the same frequency you've found before as a starting point. A low Q will flatten the curve of this filter as well.
Remark:
The VSL filters are good for repairing frequencies and for having filters for low cuts in each channel because they offer a good quality with a very low CPU consumption in the mean time.
Nevertheless: For "making sounds warmer" I would try other EQs as well. There are some just for making music warmer.
Some Freeware:
http://www.kvraudio.com/product/tdr-vos-slickeq-by-tokyo-dawn-labs/details
http://varietyofsound.wordpress.com/vst-effects/ (BootEQ mkII)
http://dsp.sonimus.com/products/soneq/
Some EQs for money:
http://spl.info/de/produkte/analog-coder-plug-ins/passeq/video.html
http://www.pspaudioware.com/plugins/equalizers/psp_nobleq/
http://www.waves.com/plugins/rs56 (...and others from waves)
http://www.plugin-alliance.com/en/plugins/detail/elysia_museq.html
...
BTW. Some of theme seem to be very expensive but all of them are "On Sale" from time to time.
So you will be able to buy it for the half price. Further on: Most of them you can try for free for some days.
Do it and you will see that it is worth to have on or more of those "legends". They really can make the race.
Best
Beat