In 2005, the Emerson String Quartet released an album of Mendelssohn’s string quartets which also included a version of the octet. Instead of partnering with another string quartet, though, they recorded it by themselves, taking great care to make it sound like a real ensemble of eight (I was particularly interested in their idea of rotating chairs).
These two videos explain the process and are an interesting micro-documentary.
Part one:
Part two:
The CD is also entirely worth owning, even if it is a little expensive:
