Well I gave it a quick try and all appears to work. My song is all midi, which I am just assuming is the only way this would work.

The real problem for me doing this is the BIAB midi synth for horns is so poor it is just hard to hear. I am assuming you need to capture the midi harmony output and transfer to a decent VST plugin. Does any of that help?

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BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, Motu Audio Express 6x6 - My SoundCloud (Tip: No need to create a SC account to hear music - just hit ESC ).