Questions for Sonus Faber owners

Simple repair, no problem. There is no need to replace the strings, they are repairable:
Carefully pull off your stringy speaker grill. Turn the grill upside down (90 degrees) and reattach it to your four speaker plugs. You'll notice a trough or small trench, where all the grill strings are tied and retained. Pull gently up on the loose string, which is surprisingly elastic.
Each string goes through two holes and appears to take up two lines/places when you look at it. Pulling gently on the string will tighten it. After pulling, retie the string now that it's tighter. The knot will be retained in the same trough from where you orginally pulled the string. If you have extra string after pulling it tighter & tieing it, snip the excess gently with a nail clipper or scisssors. The grill strings are tight now & should look new.

As with many directions, this may sound complicated. ut once you look 'em over, it'll make sense. It's easy to retighten these, but does require patience.

Hope this helps.

Rubinken, That is interesting, however, I am more concerned about how to replace the strings if necessary and not to pull them tighter. I suspect that as they age, pulling the strings tighter will not be an option as their
elasticity will fail and they will probably snap.
I am also wandering about the SF G bases as they use the same kind of strings, only a lot thicker. Does anyone have
any experience with these matters?

Did you tried ask Sonus Faber directly? They are very helpful and informative.

I still haven't heard back from SF, after requesting twice.  Must be Covid delays.

2mm wrapped rubber string.   Available at craft stores, looks identical.  Nice project for a rainy day.

Correction:   1mm.   One Sonus faber elipsa required 102 meters of elastic rubber wrapped string...

102 meters.   Tomorrow is another day.   Martini and Tony Bennett time.