This thread should include what community members have personally tested - it does not mean that NI "officially" supports the USB product as "Maschine+ compatible"... it just means that WE got something working...or not.
From what I've personally tested, the following are working with bi-directional, multi-channel audio:
Elektron Analog Rytm MK2
Elektron Digitone Keys
Tascam Model 24
RME Fireface UCX
NOT WORKING:
Presonus StudioLive 32R (booooooo! I was really hoping this would work because then I could do Maschine+ to 32R over USB, all my hardware into 32R to process and mixdown in Maschine, then stream the whole thing over AVB/Ethernet to iMac for recording without anymore DA/AD converstion or latency.
My Sweetwater sales guy told me that the Presonus Rep CONFIRMED that StudioLive 32R would work with Maschine+ over USB, but it's not looking good. Very frustrating afternoon. I thought my problems were solved!