The Ensemble Classique Köln featured on this recording probably was created for the occasion. Sextets are not easy to come by, I suppose. Performances are usually done by an existing quartet with some additions. Here the German broadcaster WDR assembled some good musicians to perform two sextets.
Especially the Glinka sextet is interesting for me. Glinka is not very well known for his chamber music; he is better known for his operas. This piece was written rather early in his life, in 1832. Not every sextet has the same instrumentation, and in this case Glinka used a double bass instead of the second cello, creating a lot fuller sound.