Thanks for quick reply.
Although not getting Bela, I guess I could control at most two audio output channels in programming via 6.35mm to 3.5mm jack adapter.
If you have a passive guitar, you can still plug that in, but the low input impedance may affect your tone and sustain.
After google "non-true-bypass pedal", I found a article that it also says "a low input impedance can cause audible signal loss". But I need some time to digest what the meaning behind.☹️ I will try to get a buffered pedal in front Bela.
There is a cheap on-board preamp on the audio input, so you could in principle connect a microphone straight into it.
Not sure where the preamp on the audio input, but I see "2 speaker amplifiers" in product page. Do you mean this?