I tried the P-125's USB audio functionality but for my environment this yields several disadvantages. First, as domzy stated, it keeps you from using your regular audio interface and you won't be able to record anything else at the same time. Second, sample rate is limited to 44.1 kHz. I much prefer using the P-125's analog output. This allows me to use my usual multichannel audio interface which has to be run at 48k (due to a Dante network). Another benefit is that I can run the analog output signal of the P-125 through my high-quality analog outboard gear prior to sending it into the multichannel audio interface to beef up the sound before recording it in Reaper.
Btw, I've created a ReaBank file for my P-125 in order to be able to select its sounds from Reaper via ReaControlMIDI. You can download the ReaBank file and a customized track template for the P-125 which provides 4 separate MIDI tracks:
https://www.audioworld.de/data/Yamaha%20P-125.reabank
https://www.audioworld.de/data/Yamah...RTrackTemplate
Put the ReaBank file into the "ReaBanks" subfolder and then open the track template.
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