I,ve sold my t4 for the new korg pax3 muzikant,i have also the Audya,
Audya is much more live on stage with huge pressure on drums and sounds,also the styles gives you an live experience.
The t4 has no pressure at al,and the eq is not deep enough,bassamples are not deep,Audya is much deeper,basedrums gives you much more pressure than the T4.
Recordings with both instruments,difference is hughes,Audya is live on cd and t4 is and still stays an home keyboard.
My opion,Yamaha go for an other direction,the tyros series are at the end of there latin.Much to expensive for what it gives.
Audyaplayer.