The alternative is an additional sound card via alsa_out: “Using multiple Sound Cards with alsa_in”
I use it to route live instruments audio in via usb to the zynthian, apply audio-fx and then back out via USB to distribute to external samplers, while keeping the native HiFiBerry Pro audio in-/out for synth layers and final mix of the output of the external samplers.
I am not sure about latency, but it works well for my purpose.