I have a Tyros 3 connected to my amplifier and speakers. If I add a second keyboard I believe I have three connection options:

One,route the Audio out of the 2nd board through the Tyros Aux input and use the Tyros as a pre-amp. This requires both keyboards to be on. Note a problem as I would likely play both and midi them together.

Two,route them both through the amp using y-audio connectors. This allows them to be on separately or together although I'm not sure the effect of feeding the amp two discrete signals.

Third, route both keyboards through a mixer that is connected to the amp. Will this degrade the sound? If not what simple mixer would you recommend?

Thanks