Duos: All the duo sonatas are worth a shot. The violin sonatas were done by the same team for Nuova Era (1+2) and Tizano (3). The sound is very dry, but realistic. The best of the viola sonata recordings was coupled with Brahms on Calliope. Of the several cello recordings, I've heard good things about the new Hyperion. The Dynamic is good, too. The Etcetera suffers from a feeble cello.
Trios: So far only trios 1-3 have been recorded. All are worth hearing. #1 is coupled with 3 on a Russian Disc recording that is a strain to listen to (all the instruments are miked point-blank), but it's your only bet for #1. Trio di Torino have done 2 and 3 for Real Sound on two separate discs, coupled with the Smetana and the Taneyev. Very good sound for both. There is a Melodiya disc of #3 along with the Op. 11 cello pieces. Of the three recordings of #3, this is by far the best. A very vivid and exciting performance that illustrates why Von Bulow was so fond of it.
String Quartets: So far only 1+2 have made it to disc, on Etcetera. If you like Mendelssohn, you'll find these charming. And enterprising quartet has posted performances of three of the four movements of the 3rd quartet on YouTube. It makes you wish for a commercial recording,
Piano Quintets: Of the several recordings of Op. 55, only the Orfeo is complete. All the others take substantial cuts in the finale. It's your best bet, but they damage the final reprise of the theme in the slow movement by taking it too fast. A better performance of that movement (and better horn playing) can be found on the old Vox LP. This quintet is full of charm and pleasant surprises. It ranks among his more sure footed works.
There is only one recording of the Op. 99. It's not one of his best, being rather episodic (like the 4th Symphony). Also, the composer is at a loss as to what to do with this quartet. They play in unison or octaves for page after page, or he pairs them such that 1st violin doubles the viola and the 2nd violin doubles the cello. 50 minutes of this is a bit much, but the work has many beautiful moments. It's on the Eda Abseits label.