Scott's ears are on target as to the Emersons' interpretations: very precise, extremely energetic, but also more than a tad bit post-modern.
While the Tokyo is certainly a classic set to treasure, if you insist on a set and only in DDD, I'd suggest you also search out the Vermeer (on Teldec). For my tastes, both the sonics and the interpretations of the Vermeer Quartet outclass the Cleveland, although I still listen to the Cleveland's versions.
If you aren't hunting for a whole set immediately, I suggest you definitely try (in DDD) the new set of Beethoven quartets still unfolding with the Takacs Q. Their 1st disc was the Op. 59 and Op. 74 quartets; that's been followed by the Op. 18. Don't know whether their late quartets, w/ Op. 95 and Grosse Fuge, is yet out; but I believe that is next on the list. Takacs is recording on Decca. Along with the Vermeer, the Takacs is my current fave rave.
Another group recording Beethoven in amazing sound which you might consider is the Leipziger Streichquartett on MDG, if you demand DDD. I'd also suggest you not avoid the analogue recordings; one can never own too many Beethoven quartet recordings. HAPPY LISTENING!