Good string sound is an ideal I have been pursuing at huge expense for the past 50 years.
As you are currently disappointed then clearly improvements may be available. However a lack of success with any genre of music may be down to any component or combination of components including how they are set up. Not knowing anything about your system aside from the fact that you have a Bartok it is difficult to go much further.
As for recordings/labels are you asking for downloads to purchase or repertoire to try via a streaming service? Unfortunately in regard to the latter at least one important independent classical label who usually offer excellent sound (Hyperion) does not allow streaming. The same for Linn Records and, I think, CPO. Other labels , such as, Channel Classics may not offer precisely the type of repertoire that you like but it is worth exploring their catalogue. Subject to repertoire that you find suitable, Harmonia Mundi can be very good.
If you care for chamber music from the earlier part of the 20th century one of my discs of the past year is this which offers superlative playing and wonderfully natural recorded sound: