The mixerr will not degrade the sound, in fact you can add EQ and fx to enhance the sound. I use a Mackie 1402 a lot of times and it does a great job as well as many other small mixers like yamaha. I mostly use a good keyboard amp because of multiple stereo inputs and srereo outs. I have a roland kc550 and it works great. There are many other good keyboard amps available as well. I personaly
would not route a secound board through the tyros or use y-connectors, even though it will work ok it's just not the best way to go. Remember, that even though you can have the best sounding keyboard and a great voice , it is only as good as the weakest link in your system. Choose a good mixer or Keyboard amp and I think you will be glad you did. Hope this helps.
KEEP JAMMIN!
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Mr. G ,OASYS , KRONOS ,Jupiter 80 , AUDYA 5, Midas Venice ,Danley Labs sm-60f's ,Danley TH mini subs, QSC KW 122's,118 sub , Senhieser and Heil , Audix VX-10 , TC_Helicon ,ZOOM 9200, Lexicon ,Alesis ,AKG solid tube ,AB international Power Sub3600