Thanks for the wonderful suggestions! Yes, "my friend" is me, hoping to expand my classical collection. As noted, Beethoven (as well as Chopin) make up a large part and I want to branch out. I do have all the lovely 3-channel LIVING STEREO sacds, though. As a keyboard player, I'm partial to all the piano-based arrangements, but the string quartets sound intriguing. . . .
The early mention of Presto led me to this -- Clarinet / cello / piano Sonatas (cheap! but sounds fun):
https://www.prestomusic.com/classical/search?search_query=BISSACD1353
And I found the Masur cycle on Discogs
Once I've digested those (and receive a few more paychecks), I'll continue on with the Grumiaux and Auryn Quartet.
Thanks again! You guys come through!