just to put some numbers on the table:
CAT USB works at 115200 bps, the FA command is 15 bytes long -> 150 bit so we can transfer more than 700 frequency set per second.
It sounds astonishing but this value is not real, because it do not consider all the management in the DUO and in the software:
to send FA we must before know the old frequency, than compute a new one and then send this new value.
This is at least two transfers (FA; to read FAxxxxxxxxxxxx; to set) withe the related sync.
I know this because I've seen this problem in EladRemote.
Of course using SW2 on a modern PC can make things really different, so it is interesting to make a test (at least through VSPE).
In any case the problem is not in the USB or in the serial protocol, but in the managemento of the UI in the DUO (standalone)
From protocol point of view: TMATE2 uses a protocol for HID through USB so the speed should not be different from other devices using MIDI through USB, but we can test.
The intersting thing about MIDI is it is substantially a simple serial protocol, not difficult to implement.
Giovanni - HB9EIK